Could be a favorite book, movie, album, game, tv show, play, concert, meme, event, news item, thing that someone said, personal achievement... whatever.
Normally I don't like trying to decide because it's not so clear. But my favorite album from 2011 is Ernst Karel's "Swiss Mountain Transport Systems." It's so... different. Ambient, both quiet and startling, not composed or performed but just beautifully recorded.
As far as movies go, I was not blown away by the Pirates move, was somewhat entertained by Harry Potter and Thor, so I guess I'd have to pick X-Men First Class. Not a great year. I've been told I should see Sucker Punch though.
As for reading, I am so far behind that even guessing what years my reading pile date from is futile. But the non-fiction book I read this year that most stands out is "Delusions of Gender."
Favorite concert was Kodo in Bloomington, Indiana. If I keep playing taiko the rest of my life and get twice as good every year until I can't lift bachi anymore, I'll never catch up with them.