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 21
2014
November 24
2014
Singed AugmentedCircle Augmented Singed [S|L] - 50% off
Lux SpellthiefCircle Spellthief Lux [S|L] - 50% off
Graves HiredGunCircle Hired Gun Graves [S|L] - 50% off
[1]
November 25
2014
November 28
2014
Vayne DragonslayerCircle Dragonslayer Vayne [S|L] - 50% off
Sejuani BearCavalryCircle Bear Cavalry Sejuani [S|L] - 50% off
Rammus FreljordCircle Freljord Rammus [S|L] - 50% off
[2]
November 28
2014
December 1
2014
Xin Zhao WingedHussarCircle Winged Hussar Xin Zhao [S|L] - 50% off
Pantheon PerseusCircle Perseus Pantheon [S|L] - 50% off
Shyvana BoneclawCircle Boneclaw Shyvana [S|L] - 50% off
[3]
December 2
2014
December 5
2014
Tryndamere SultanCircle Sultan Tryndamere [S|L] - 50% off
Syndra JusticarCircle Justicar Syndra [S|L] - 50% off
Warwick BigBadCircle Big Bad Warwick [S|L] - 50% off
[4]
December 5
2014
December 8
2014
Elise DeathBlossomCircle Death Blossom Elise [S|L] - 50% off
Garen RuggedCircle Rugged Garen [S|L] - 50% off
Trundle Lil'SluggerCircle Lil' Slugger Trundle [S|L] - 50% off
[5]
December 9
2014
December 12
2014
Annie ReverseCircle Reverse Annie [S|L] - 50% off
Jarvan IV WarringKingdomsCircle Warring Kingdoms Jarvan IV [S|L] - 50% off
Nasus PharaohCircle Pharaoh Nasus [S|L] - 50% off
[6]
December 12
2014
December 15
2014
Zyra WildfireCircle Wildfire Zyra [S|L] - 50% off
Wukong GeneralCircle General Wukong [S|L] - 50% off
Master Yi ChosenCircle Chosen Master Yi [S|L] - 50% off
[7]
December 16
2014
December 19
2014
Rengar HeadhunterCircle Headhunter Rengar [S|L] - 50% off
Pantheon FullMetalCircle Full Metal Pantheon [S|L] - 50% off
Shaco RoyalCircle Royal Shaco [S|L] - 50% off
[8]
December 19
2014
December 22
2014
Renekton BloodfuryCircle Bloodfury Renekton [S|L] - 50% off
Morgana BladeMistressCircle Blade Mistress Morgana [S|L] - 50% off
Orianna GothicCircle Gothic Orianna [S|L] - 50% off
[9]
December 23
2014
December 26
2014
Lee Sin DragonFistCircle Dragon Fist Lee Sin [S|L] - 50% off
Nautilus AstroNautilusCircle AstroNautilus [S|L] - 50% off
Nidalee PharaohCircle Pharaoh Nidalee [S|L] - 50% off
[10]
December 26
2014
December 29
2014
Ahri PopstarCircle Popstar Ahri [S|L] - 50% off
Leona DefenderCircle Defender Leona [S|L] - 50% off
Zilean GroovyCircle Groovy Zilean [S|L] - 50% off
[11]
December 30
2014
January 2
2015
Gangplank SultanCircle Sultan Gangplank [S|L] - 50% off
Soraka CelestineCircle Celestine Soraka [S|L] - 50% off
Irelia AviatorCircle Aviator Irelia [S|L] - 50% off
[12]
January 2
2015
January 5
2015
Olaf PentakillCircle Pentakill Olaf [S|L] - 50% off
Karma SunGoddessCircle Sun Goddess Karma [S|L] - 50% off
Lux CommandoCircle Commando Lux [S|L] - 50% off
[13]
January 6
2015
January 9
2015
Katarina BilgewaterCircle Bilgewater Katarina [S|L] - 50% off
Viktor CreatorCircle Creator Viktor [S|L] - 50% off
Twisted Fate JackofHeartsCircle Jack of Hearts Twisted Fate [S|L] - 50% off
[14]
January 9
2015
January 12
2015
Yorick PentakillCircle Pentakill Yorick [S|L] - 50% off
Taric ArmoroftheFifthAgeCircle Armor of the Fifth Age Taric [S|L] - 50% off
Galio CommandoCircle Commando Galio [S|L] - 50% off
[15]
January 13
2015
January 16
2015
Shen WarlordCircle Warlord Shen [S|L] - 50% off
Yasuo HighNoonCircle High Noon Yasuo [S|L] - 50% off
Udyr BlackBeltCircle Black Belt Udyr [S|L] - 50% off
[16]
January 16
2015
January 19
2015
Nami KoiCircle Koi Nami [S|L] - 50% off
Volibear NorthernStormCircle Northern Storm Volibear [S|L] - 50% off
Xin Zhao ImperialCircle Imperial Xin Zhao [S|L] - 50% off
[17]
January 20
2015
January 23
2015
Draven GladiatorCircle Gladiator Draven [S|L] - 50% off
Garen SteelLegionCircle Steel Legion Garen [S|L] - 50% off
Vayne AristocratCircle Aristocrat Vayne [S|L] - 50% off
[18]

References

LoL's Official Sales page