SPOILER WARNING FOR THOSE WHO HAVE NOT READ THE BOOKS!
Alright, here's this mammoth of a death list, with cause of death. Let me know if I missed anything or got anything wrong.
POV characters are bolded, royalty (incl. claimants and former royalty) is italicized
=A GAME OF THRONES=
Ser Waymar Royce - Killed by the Others
Will - Strangled by Waymar Royce
Gared - Beheaded with Ice by Eddard Stark
Lord Jon Arryn - Poisoned with tears of Lys by Lysa Arryn
Mycah - Cut down by Sandor Clegane
Lady - Cut down with Ice by Eddard Stark
Ser Hugh of the Vale - Lanced in the throat by Gregor Clegane
Jyck - Cut down by a mountain clansman
Kurleket - Maced in the face by a mountain clansman
Mohor - Slain by mountain clansmen
Morrec - Died of a festered wound
Chiggen - Throat slit by Bronn as a "mercy" kill
Lharys - Slain by mountain clansmen
Heward - Slain by Lannister guardsmen
Wyl - Slain by Lannister guardsmen
Jory Cassel - Slain by Lannister guardsmen
Hali - Torn in the belly by Summer
Wallen - Killed by Grey Wind
Stiv - Shot with an arrow by Theon Greyjoy
Tregar - Killed by Eddard Stark
Ser Vardis Egen - Killed by Bronn
Prince Viserys Targaryen - Crowned with molten gold by Drogo
King Robert Baratheon - Gored by a boar
Tomard - Slain by gold cloaks
Varly - Slashed in the throat by Janos Slynt
Cayn - Slain by Sandor Clegane
Desmond - Slain by gold cloaks or Lannister guardsmen
Hullen - Killed by gold cloaks or Lannister guardsmen
Syrio Forel - Killed by Meryn Trant
Porther - Unknown causes
Othor - Killed by the Others, burned by Jon Snow
Jafer Flowers - Killed by an axe blow to the neck (presumably by wights), cut to pieces
Lord Vance - Died in battle against the westerlands army
Ser Raymun Darry - Died in battle against Gregor Clegane's host
Masha Heddle - Hanged by Tywin Lannister
Ser Jaremy Rykker - Stabbed in the bowels by Jafer Flowers
Khal Ogo - Slain by Drogo
Khal Fogo - Slain by Drogo
Ulf son of Ulmar - Died in battle against the northern army
Conn son of Coratt - Speared by a northman
Lord Halys Hornwood - Died in battle against the westerlands army
Eddard Karstark - Killed by Jaime Lannister
Torrhen Karstark - Killed by Jaime Lannister
Daryn Hornwood - Killed by Jaime Lannister
Quaro - Killed by Qotho
Qotho - Killed by Jorah Mormont
Haggo - Killed by Rakharo and Jhogo
Ko Cohollo - Shot with an arrow by Aggo
Lord Eddard Stark - Beheaded with Ice by Ilyn Payne
Septa Mordane - Killed by gold cloaks or Lannister guardsmen
Vayon Poole - Killed by gold cloaks or Lannister guardsmen
Khalakka Rhaego - Stillborn
Eroeh - Throat cut by Mago or Jhaqo
Khal Drogo - Smothered by Daenerys Targaryen
Lord Andros Brax - Drowned after his raft was hit by a catapult
Mirri Maz Duur - Burned by Daenerys Targaryen
=A CLASH OF KINGS=
Maester Cressen - Poisoned himself with the strangler
Praed - Unknown causes (had a persistent cough)
Ser Burton Crakehall - Slain by the brotherhood without banners
Lyman Darry - Killed by the Mountain's men
Barra - Killed by Allar Deem
Allar Deem - Drowned by one of his escorts
Doreah - Died of a wasting disease
Woth - Speared in the neck by a man-at-arms
Dobber - Stabbed in the belly by a man-at-arms
Qyle - Maced in the face by a knight
Koss - Cut down by Amory Lorch's men
Kurz - Died of a festered wound
Yoren - Axed in the head by Amory Lorch's men
Lommy Greenhands - Speared in the throat by Rafford
Lord Renly Baratheon - Cut down by a shadow
Ser Robar Royce - Killed by Loras Tyrell
Ser Emmon Cuy - Killed by Loras Tyrell
Ser Stevron Frey - Died of a festered wound
Ser Stafford Lannister - Lanced by Rickard Karstark
Chiswyck - Pushed off a wall by Jaqen H'ghar
Benfred Tallhart - Drowned by Aeron Greyjoy
Weese - Throat torn out and face eaten by his spotted dog, loosed by Jaqen H'ghar
The High Septon - Ripped apart by an angry mob
Ser Preston Greenfield - Repeatedly stabbed and hacked by an angry mob
Ser Aron Santagar - Skull smashed with a stone by an angry mob
Alfyn Crowkiller - Killed by Qhorin Halfhand
Ser Cortnay Penrose - Killed by a shadow
Lord Leo Lefford - Drowned in battle against the westerlands army
Lady Donella Hornwood - Died of starvation or bled out
Alebelly - Killed by Theon Greyjoy's men
Mikken - Executed by Stygg
Ser Amory Lorch - Torn apart by a bear
Septon Chayle - Drowned by Theon Greyjoy
Drennan - Throat cut by Osha
Squint - Killed by Summer and Shaggydog
Gelmarr the Grim - Thrown down stairs by Ramsay Snow
Aggar - Throat cut by Ramsay Snow
Gynir Rednose - Drowned by Ramsay Snow
Farlen - Executed by Theon Greyjoy
Ser Imry Florent - Burned with wildfire by Tyrion Lannister
Allard Seaworth - Died in battle against the royal fleet
Dale Seaworth - Drowned in battle against the royal fleet
Matthos Seaworth - Burned with wildfire by Tyrion Lannister
Maric Seaworth - Burned with wildfire by Tyrion Lannister
Lord Chyttering - Burned with wildfire by Tyrion Lannister
Lord Monford Velaryon - Burned with wildfire by Tyrion Lannister
Ser Mandon Moore - Drowned by Podrick Payne
Lord Bryce Caron - Slain by Ser Philip Foote
Ser Guyard Morrigen - Slain by Garlan Tyrell
Lord Guncer Sunglass - Burned by Selyse Florent
Maester Tothmure - Executed by Roose Bolton
Ser Rodrik Cassel - Slain by Ramsay Snow
Lord Cley Cerwyn - Shot in the eye with an arrow
Leobald Tallhart - Died in battle against Ramsay Snow's host
Red Rolfe - Killed by Ramsay Snow's men
Kenned the Whale - Killed by Ramsay Snow's men
Ulf the Ill - Killed by Ramsay Snow's men
Poxy Tym - Axed in the face
Black Lorren - Killed by Ramsay Snow's men
Squire Dalbridge - Killed by wildlings
Ebben - Killed by Rattleshirt's men
Qhorin Halfhand - Killed with Longclaw by Jon Snow
Maester Luwin - Mercy killed by Osha
=A STORM OF SWORDS=
Chett - Killed by the Others
Iggo - Arm ripped off by Nymeria
Lord Jacelyn Bywater - Shot in the throat with an arrow by gold cloaks
Jate Blackberry - Unknown causes
Hookface Will - Unknown causes
Hal the Hog - Unknown causes
Maslyn - Slain by a wight
Thoren Smallwood - Head ripped off by a wight bear
Brown Bernarr - Killed by wights
Ser Ottyn Wythers - Kicked in the face by a horse
Small Paul - Killed by an Other, burned by Samwell Tarly
Ser Helman Tallhart - Died in battle against Randyll Tarly's host
Delp - Killed by Rickard Karstark
Elwood - Killed by Rickard Karstark
Tion Frey - Killed by Rickard Karstark
Willem Lannister - Killed by Rickard Karstark
Lord Rickard Karstark - Beheaded by Robb Stark
Master Kraznys mo Nakloz - Burned by Drogon
Master Grazdan mo Ullhor - Shot in the mouth with an arrow by Rakharo
Ser Cleos Frey - Shot with arrows by outlaws
Jarl - Fell off the Wall during a climb, impaled on a tree
Symon Silver Tongue - Killed by Bronn
Bannen - Died of a festered wound
Craster - Throat slit by Dirk
Garth of Oldtown - Killed by Garth of Greenaway
Rolley of Sisterton - Fell and broke his neck
Ser Byam Flint - Unknown causes, possibly suffocated by Craster's corpse
Lord Jeor Mormont - Slain by Ollo Lophand
Alyn of Winterfell - Killed by Lannister men
Lord Hoster Tully - Died of a long illness
King Balon IX Greyjoy - Thrown off a bridge by an assassin hired or commanded by Euron Greyjoy
Lord Sawane Botley - Drowned by Euron Greyjoy
Ser Kyle - Impaled with a spear by a Bloody Mummer
Septon Utt - Hanged by the brotherhood without banners
Lark the Sisterman - Killed by the Others
Ryles - Killed by the Others
Softfoot - Killed by the Others
Prendahl na Ghezn - Killed by Daario Naharis
Sallor the Bald - Killed by Daario Naharis
Robin Flint - Stabbed repeatedly by Freys
Ser Wendel Manderly - Shot in the mouth with a crossbow
Lucas Blackwood - Slain by Hosteen Frey
Ser Donnel Locke - Shot with crossbows
Owen Norrey - Shot with crossbows
Dacey Mormont - Axed in the belly by Ryman Frey
Smalljon Umber - Beheaded by a Bolton or Karstark man
King Robb Stark - Stabbed in the heart by Roose Bolton
Aegon Frey - Throat sawed by Catelyn Stark
Lady Catelyn Stark - Throat slit by Raymund Frey
Ser Garse Goodbrook - Killed by Grey Wind
Ser Tytos Frey - Killed by Grey Wind
Ser Raynald Westerling - Shot with a crossbow (supposedly died, body not found)
Grey Wind - Shot with crossbows
Dick Follard - Shot with an arrow by Ygritte
Rast - Speared by a Thenn
Young Henly - Died in battle against the wildlings
Old Henly - Died in battle against the wildlings
Dornish Dilly - Speared between the shoulder blades by a Thenn
Magnar Styr of Thenn - Fell off the Wall
Quort - Died in battle against the Night's Watch
Stone Thumbs - Died in battle against the Night's Watch
Ygritte - Shot with an arrow by a Night's Watchman
Oznak zo Pahl - Killed by Strong Belwas
Mero of Braavos - Torn apart by freedmen
King Joffrey Baratheon - Poisoned with the strangler by Olenna Tyrell
Ser Dontos Hollard - Shot with crossbows by Petyr Baelish's men
Lord Vargo Hoat - Cut to pieces by Gregor Clegane
Donal Noye - Spine crushed by Mag Mar Tun Doh Weg
Mag Mar Tun Doh Weg - Impaled through the throat by Donal Noye
Ser Endrew Tarth - Died in battle against the wildlings
Ser Aladale Wynch - Died in battle against the wildlings
Red Alyn of the Rosewood - Fell off the Wall
Prince Oberyn Nymeros Martell - Skull smashed by Gregor Clegane
Orell - Burned by Melisandre (as an eagle)
Harma Dogshead - Died in battle against the Dragonstone army
Dormund - Cut down by Richard Horpe
Polliver - Slain by Sandor Clegane
The Tickler - Repeatedly stabbed by Arya Stark
Watt of Long Lake - Axed in the skull by a wildling
Dalla - Died in childbirth
Shae - Strangled with a Hand chain by Tyrion Lannister
Lord Tywin Lannister - Shot with a crossbow by Tyrion Lannister
Lord Eon Hunter - Murdered by Harlan Hunter
Lady Lysa Arryn - Thrown through the Moon Door by Petyr Baelish
Lord Beric Dondarrion - Gave Catelyn Stark the flame of life (final death)
Petyr Frey - Hanged by the brotherhood without banners
Merrett Frey - Hanged by the brotherhood without banners
=A FEAST FOR CROWS=
Pate - Poisoned by a Faceless Man
Dick Crabb - Face smashed with a morningstar by Shagwell the Fool
Pyg - Killed by Brienne of Tarth
Timeon of Dorne - Killed by Brienne of Tarth
Shagwell the Fool - Stabbed by Brienne of Tarth
Senelle - Experimented on by Qyburn
Ser Arys Oakheart - Axed by Areo Hotah
Marillion - Died in a sky cell
Lord Baelor Blacktyde - Cut into seven pieces by Euron Greyjoy's crew
Ser Talbert Serry - Drowned after being thrown overboard by Victarion Greyjoy
Ser Balman Byrch - Stabbed in the eye by Bronn
Lady Falyse Stokeworth - Experimented on by Qyburn
Dareon - Throat slit by Arya Stark
Maester Aemon - Died of a chill
Lady Tanda Stokeworth - Died of a chill
Rorge - Killed by Brienne of Tarth
Biter - Speared in the neck by Gendry
Lord Gyles Rosby - Died of a long sickness
Ser Ryman Frey - Hanged by the brotherhood without banners
=A DANCE WITH DRAGONS=
Thistle - Killed by wights
Varamyr Sixskins - Died after attempting to steal Thistle's body
Stalwart Shield - Killed by the Sons of the Harpy
Hazzea - Burned by Drogon
Janos Slynt - Beheaded with Longclaw by Jon Snow
Dirk - Killed by Coldhands
Ollo Lophand - Killed by Coldhands
Clubfoot Karl - Killed by Coldhands
Lord Alester Florent - Burned by Melisandre
Kyra - Killed by Ramsay Snow
Rattleshirt - Burned by Melisandre
Mossador - Crushed by stones dropped by Sons of the Harpy
Duran - Crushed by stones dropped by Sons of the Harpy
Captain Ralf Kenning - Mercy killed by Theon Greyjoy
Dagon Codd - Axed by Adrack Humble
Adrack Humble - Flayed by Ramsay Snow
Hagen the Horn - Shot with an arrow by a northman
Rolfe the Dwarf - Beheaded in battle against the Dragonstone army
Captain Quenton Greyjoy - Axed by a northern mountain clansman
Oppo - Killed by sailors
Jack Bulwer - Killed by the Weeper
Hairy Hal - Killed by the Weeper
Garth Greyfeather - Killed by the Weeper
Ser Jared Frey - Baked into a pie by Wyman Manderly
Symond Frey - Baked into a pie by Wyman Manderly
Rhaegar Frey - Baked into a pie by Wyman Manderly
Lord Harwood Fell - Died of a fever
Yellow Dick - Murdered
Little Walder Frey - Murdered
Luton - Speared in the chest by Ramsay Bolton
Holly - Slain by Bolton men
Barsena Blackhair - Ripped open by a boar
Master Yurkhaz zo Yunzak - Trampled, or died of cardiac arrest
Torwynd the Tame - Froze to death, slain by Tormund
Hamish the Harper - Breathing difficulties
Maester Kerwin - Killed by Victarion Greyjoy
Nurse - Poisoned with mushrooms by Tyrion Lannister
Lord Admiral Groleo - Killed by Bloodbeard
Master Yezzan zo Qaggaz - Died of the bloody flux
Cromm - Died of his wounds after a battle
Khrazz - Slain by Barristan Selmy
Rowan - Flayed by Ramsay Bolton
Squirrel - Flayed by Ramsay Bolton
Willow Witch-eye - Flayed by Ramsay Bolton
Frenya - Flayed by Ramsay Bolton
Myrtle - Flayed by Ramsay Bolton
Ser Patrek of King's Mountain - Killed by Wun Weg Wun Dar Wun
Lord Jon Snow - Presumably died after being stabbed by his men
Prince Quentyn Nymeros Martell - Burned by Rhaegal
Grand Maester Pycelle - Killed by Varys
Ser Kevan Lannister - Shot in the chest with a crossbow by Varys and finished off by the little birds
=THE WINDS OF WINTER=
Rafford - Throat and femoral artery cut by Arya Stark
Total deaths: 277