Lots of prolific writers who I admire/have "grown up" reading and watching have died this year (Richard Holmes & Christopher Hitchens immediately spring to mind, but some others as well). But I'm a mere youngling so it probably made a bit more of an impression on me. Meaning no disrespect, I get the impression I'm a little bit less used to familiar figures/influences dying than other ABers might be :P.
The riots for me were easily the most fascinating thing to happen in 2011, albeit in an uncomfortable way. In terms of current affairs, it's probably them and the Arab Spring I'll mostly remember the year for. (I had no interest at all in the Royal Wedding so I probably won't remember the year for it). Feels a bit weird to isolate them though as the year has been extremely eventful both for me and the world, and like most people I'm far more likely to remember the year for events in my own life.
I think 2011 does quite well to demonstrate the Chinese proverb about the misfortune of living in interesting times, though... (Forgive the paraphrasing, I can't remember the exact wording).