MvC3 actually consistently had some sort of official showing every month from it's reveal until release:
April 2010 - Revealed
May 2010 - First screenshots revealed in Game Informer (Also confirmed Dante, Deadpool, Captain America, Felicia, though they weren't shown in-game until...)
June 2010 - E3, the above characters officially shown off, Dormammu teased
July 2010 - SDCC, Super Skrull, Trish, Doom & Chun Li, Ammy & Thor revealed
August 2010 - Gamescom, Viewtful Joe & Dormammu reealed
Sep 2010 - TGS, Wesker, Spidey, X-23 & Tron revealed
Oct 2010 - Spencer, Arthur, Magneto & MODOK revealed
Nov 2010 - She Hulk & Zero, Shuma and Jill revealed as DLC along with the Limited Edition
Dec 2010 - Viper & Storm
Jan 2011 - Pretty much everyone else
Feb 2011 - Released
I remember the wait between news seeming like forever, but looking back, that was actually an amazingly consistent reveal schedule.