The list is ordered from the oldest to the most recent announcement made by the Riot staff regarding skin sales.

Pre-Seasons Seasons
Pre-Season One Season One
Pre-Season Two Season Two
Pre-Season Three Season Three
Pre-Season Four Season Four
Pre-Season Five Season Five
Pre-Season Six Season Six
Pre-Season Seven Season Seven
Pre-Season Eight Season Eight
Early Sales


Period Sales Link
November 20
2012
November 23
2012
Shaco RoyalCircle Royal Shaco [S|L] - 50% off
Renekton RuneWarsCircle Rune Wars Renekton [S|L] - 50% off
Udyr PrimalCircle Primal Udyr [S|L] - 50% off
[1]
November 23
2012
November 26
2012
Irelia FrostbladeCircle Frostblade Irelia [S|L] - 50% off
Ashe AmethystCircle Amethyst Ashe [S|L] - 50% off
Miss Fortune CowgirlCircle Cowgirl Miss Fortune [S|L] - 50% off
[2]
November 27
2012
November 30
2012
Graves JailbreakCircle Jailbreak Graves [S|L] - 50% off
Varus BlightCrystalCircle Blight Crystal Varus [S|L] - 50% off
Garen RuggedCircle Rugged Garen [S|L] - 50% off
[3]
November 30
2012
December 3
2012
Darius LordCircle Lord Darius [S|L] - 50% off
Talon RenegadeCircle Renegade Talon [S|L] - 50% off
Cho'Gath JurassicCircle Jurassic Cho'Gath [S|L] - 50% off
[4]
December 3
2012
December 7
2012
Diana DarkValkyrieCircle Dark Valkyrie Diana [S|L] - 50% off
Lulu BittersweetCircle Bittersweet Lulu [S|L] - 50% off
Nunu DemolisherCircle Demolisher Nunu [S|L] - 50% off
Olaf GlacialCircle Glacial Olaf [S|L] - 50% off
Ezreal FrostedCircle Frosted Ezreal [S|L] - 50% off
[5]
December 7
2012
December 10
2012
Viktor FullMachineCircle Full Machine Viktor [S|L] - 50% off
Cassiopeia DesperadaCircle Desperada Cassiopeia [S|L] - 50% off
Singed AugmentedCircle Augmented Singed [S|L] - 50% off
[6]
December 11
2012
December 14
2012
Searing Seeds:
Zyra WildfireCircle Wildfire Zyra [S|L] - 50% off
Warwick FirefangCircle Firefang Warwick [S|L] - 50% off
Wukong VolcanicCircle Volcanic Wukong [S|L] - 50% off
[7]
December 14
2012
December 17
2012
Ice Fort War:
Janna FrostQueenCircle Frost Queen Janna [S|L] - 50% off
Malphite GlacialCircle Glacial Malphite [S|L] - 50% off
Annie FrostfireCircle Frostfire Annie [S|L] - 50% off
[8]
December 18
2012
January 6
2013
Opening the Legacy Skin Vault - Legacy skins previously removed from the store:
Heimerdinger AlienInvaderCircle Alien Invader Heimerdinger [S|L] - 50% off
Jax AnglerCircle Angler Jax [S|L] - 50% off
Annie AnnieinWonderlandCircle Annie in Wonderland [S|L] - 50% off
Teemo BadgerCircle Badger Teemo [S|L] - 50% off
Poppy BlacksmithCircle Blacksmith Poppy [S|L] - 50% off
Urgot ButcherCircle Butcher Urgot [S|L] - 50% off
Akali CrimsonCircle Crimson Akali [S|L] - 50% off
Garen DesertTrooperCircle Desert Trooper Garen [S|L] - 50% off
Mordekaiser DragonKnightCircle Dragon Knight Mordekaiser [S|L] - 50% off
Taric EmeraldCircle Emerald Taric [S|L] - 50% off
Warwick FeralCircle Feral Warwick [S|L] - 50% off
Tristana FirefighterCircle Firefighter Tristana [S|L] - 50% off
Shen FrozenCircle Frozen Shen [S|L] - 50% off
Sion HextechCircle Hextech Sion [S|L] - 50% off
Tryndamere HighlandCircle Highland Tryndamere [S|L] - 50% off
Twitch KingpinCircle Kingpin Twitch [S|L] - 50% off
Nidalee LeopardCircle Leopard Nidalee [S|L] - 50% off
Evelynn MasqueradeCircle Masquerade Evelynn [S|L] - 50% off
Alistar MatadorCircle Matador Alistar [S|L] - 50% off
Dr. Mundo Mr.MundoverseCircle Mr. Mundoverse [S|L] - 50% off
Cho'Gath NightmareCircle Nightmare Cho'Gath [S|L] - 50% off
Ezreal NottinghamCircle Nottingham Ezreal [S|L] - 50% off
Poppy NoxusCircle Noxus Poppy [S|L] - 50% off
Karthus PhantomCircle Phantom Karthus [S|L] - 50% off
Amumu PharaohCircle Pharaoh Amumu [S|L] - 50% off
Ryze ProfessorCircle Professor Ryze [S|L] - 50% off
Corki RedBaronCircle Red Baron Corki [S|L] - 50% off
Annie RedRidingCircle Red Riding Annie [S|L] - 50% off
Caitlyn SafariCircle Safari Caitlyn [S|L] - 50% off
Nunu SasquatchCircle Sasquatch Nunu [S|L] - 50% off
Gragas ScubaCircle Scuba Gragas [S|L] - 50% off
Malphite ShamrockCircle Shamrock Malphite [S|L] - 50% off
Kog'Maw SonoranCircle Sonoran Kog'Maw [S|L] - 50% off
Sivir SpectacularCircle Spectacular Sivir [S|L] - 50% off
Kennen SwampMasterCircle Swamp Master Kennen [S|L] - 50% off
Twisted Fate TheMagnificentCircle The Magnificent Twisted Fate [S|L] - 50% off
Zilean TimeMachineCircle Time Machine Zilean [S|L] - 50% off
Dr. Mundo ToxicCircle Toxic Dr. Mundo [S|L] - 50% off
Kayle UnmaskedCircle Unmasked Kayle [S|L] - 50% off
Malzahar VizierCircle Vizier Malzahar [S|L] - 50% off
Shaco WorkshopCircle Workshop Shaco [S|L] - 50% off
Shen YellowJacketCircle Yellow Jacket Shen [S|L] - 50% off
[9]
December 21
2012
December 24
2012
Fiora NightravenCircle Nightraven Fiora [S|L] - 50% off
Soraka DivineCircle Divine Soraka [S|L] - 50% off
Ahri MidnightCircle Midnight Ahri [S|L] - 50% off
[10]
December 25
2012
December 28
2012
Save Snowdown!
Volibear NorthernStormCircle Northern Storm Volibear [S|L] - 50% off
Caitlyn ArcticWarfareCircle Arctic Warfare Caitlyn [S|L] - 50% off
Kennen ArcticOpsCircle Arctic Ops Kennen [S|L] - 50% off
[11]
December 28
2012
December 31
2012
Beach Bust:
Singed SurferCircle Surfer Singed [S|L] - 50% off
Teemo PandaCircle Panda Teemo [S|L] - 50% off
Rumble RumbleintheJungleCircle Rumble in the Jungle [S|L] - 50% off
[12]
December 31
2012
January 4
2013
Cassiopeia MythicCircle Mythic Cassiopeia [S|L] - 50% off
Ezreal ExplorerCircle Explorer Ezreal [S|L] - 50% off
Gragas Gragas,Esq.Circle Gragas, Esq. [S|L] - 50% off
[13]
January 4
2013
January 7
2013
Kassadin HarbingerCircle Harbinger Kassadin [S|L] - 50% off
Malzahar OverlordCircle Overlord Malzahar [S|L] - 50% off
Cho'Gath LochNessCircle Loch Ness Cho'Gath [S|L] - 50% off
[14]
January 8
2013
January 11
2013
Tristana GuerillaCircle Guerilla Tristana [S|L] - 50% off
Teemo ReconCircle Recon Teemo [S|L] - 50% off
Corki UrfriderCircle Urfrider Corki [S|L] - 50% off
[15]
January 11
2013
January 14
2013
Skin Super Sale:
Sona GuqinCircle Guqin Sona [S|L] - 50% off
Talon DragonbladeCircle Dragonblade Talon [S|L] - 50% off
Lee Sin DragonFistCircle Dragon Fist Lee Sin [S|L] - 50% off
Wukong JadeDragonCircle Jade Dragon Wukong [S|L] - 50% off
Vayne HeartseekerCircle Heartseeker Vayne [S|L] - 50% off
Fizz FishermanCircle Fisherman Fizz [S|L] - 50% off
Riven BattleBunnyCircle Battle Bunny Riven [S|L] - 50% off
Morgana BlackthornCircle Blackthorn Morgana [S|L] - 50% off
Swain TyrantCircle Tyrant Swain [S|L] - 50% off
Amumu SadRobotCircle Sad Robot Amumu [S|L] - 50% off
Shyvana DarkflameCircle Darkflame Shyvana [S|L] - 50% off
Pantheon GlaiveWarriorCircle Glaive Warrior Pantheon [S|L] - 50% off
[16]
January 15
2013
January 18
2013
Xerath ScorchedEarthCircle Scorched Earth Xerath [S|L] - 50% off
Galio HextechCircle Hextech Galio [S|L] - 50% off
Shen SurgeonCircle Surgeon Shen [S|L] - 50% off
[17]
January 18
2013
January 21
2013
Heimerdinger PiltoverCustomsCircle Piltover Customs Heimerdinger [S|L] - 50% off
Corki HotRodCircle Hot Rod Corki [S|L] - 50% off
Zilean GroovyCircle Groovy Zilean [S|L] - 50% off
[18]
January 22
2013
January 25
2013
Talon CrimsonEliteCircle Crimson Elite Talon [S|L] - 50% off
Riven CrimsonEliteCircle Crimson Elite Riven [S|L] - 50% off
Draven SoulReaverCircle Soul Reaver Draven [S|L] - 50% off
[19]
January 25
2013
January 28
2013
Taric ArmoroftheFifthAgeCircle Armor of the Fifth Age Taric [S|L] - 50% off
Mordekaiser InfernalCircle Infernal Mordekaiser [S|L] - 50% off
Nasus DreadknightCircle Dreadknight Nasus [S|L] - 50% off
[20]
January 29
2013
February 1
2013
Common Criminals:
Gragas VandalCircle Vandal Gragas [S|L] - 50% off
Vladimir VandalCircle Vandal Vladimir [S|L] - 50% off
Twitch VandalCircle Vandal Twitch [S|L] - 50% off
Twitch VandalCircle Vandal Twitch [S|L] - 50% off
Brand VandalCircle Vandal Brand [S|L] - 50% off
[21]

References

Skin Sales Super-Thread by Coreporeal