Kalista release date: 2014-10-31, but i think they change it.

As far as I know, Kalista, an ad carry, is coming to League seeking for revenge on several champions who are marked with shrouded profile pages. 
Kalista has a completely new mechanic named soulbond which link you with a chosen teammate, often your support. He/she uses spears. Thank me later.

Upcoming champions: Ao Shin (mid), Thoridus (looks like jungler/top), Nervia (Support) Skins: Exterminator Twitch, Debonair Braum, Debonair LeBlanc - LB mid 2015. will update it-,^

UPDATE1: Reworks 2015: Shaco(End 2014/january 2015), Poppy(VU+Rework), Fiora, Vladimir (VU+Rework), Gangplank,Warwick (VU+Rework), Nunu (VU+Rework) (and propably Teemo but it's not confirmed)

UPDATE2: Skins 2015(not all ofc): Torturer Sion, Arclight Thresh, Hextech Jayce, Prehistoric Gnar, Void Varus <- Not final names i think but it's all what i know

UPDATEv2: 2015 planned skins: Malzahar, Lee Sin, Kayle, Gragas, Darius , Azir, Akali, Elise, Vel'koz, Zyra, Xin Zhao, Zilean, Vi, Katarina, Janna, Jinx, Garen, Cho'gath and many more.

UPDATE3: Ultimate 2014 is not for Sona, they think about Xerath/Lux. <- NOT 100%

UPDATE4: Buffs in next months: Yasuo, Elise, Kassadin, Gragas, Shen, Shyvana, Azir, Cassiopeia, Kennen - (not all champions, not confirmed 100%, they can change it)

Nerfs/balances in next months: Rammus, Irelia, Ryze, Kha(not sure), Fizz, Nami, Syndra, Zed (not all, not confirmed 100%, they can change it)

PS: Zed is Nocturne before "transformation".