Quick summary of GW releases from 2011:
Jan: Skaven hellpit and lightning cannon
Feb: Blood Angels Storm Raven & dread
March: Orcs Arachnarok & Savage orcs
April: Grey Knights infantry and dreadknight
May: Tomb Kings Necrosphinx & others
June: Dark Eldar Razorwing, Venom, Talos, Scourges
July: Storm of magic monsters, fulcrums & wizards
August: Vampires Terrorgheist & others
September: Ogre Kingdoms Thundertusk, Ironblaster & Mournfangs
October: Dreadfleet
November: Necrons
December: Beastmen
My vote goes to the necrosphinx, even though I don't play tomb kings, really sets the bar for cramming lots of stuff into a multi-purpose kit: