Sony has published its list of PlayStation Network best-sellers for 2011. In terms of downloadable stuff, you won't be surprised to see loads of Call of Duty maps and the like. In terms of games, well, take a look at this hardcore chart.
Top PSN Games of 2011 (by units sold, digital games only, not full PS3 games)
Tetris
Resident Evil 4
Infamous Festival of Blood
Back to the Future: The Game - Full Series
Dungeon Hunter: Alliance
Castle Crashers
Limbo
Battlefield 1943
Mortal Kombat Arcade Kollection
Magic: The Gathering - Duels of the Planeswalkers 2012
Top paid PlayStation Store downloads (including paid PS Plus offerings)
Call of Duty: Black Ops First Strike
Call of Duty: Black Ops Escalation: Content Pack 2
Call of Duty: Black Ops Annihilation: Content Pack 3
MLB 11 The Show Road to the Show Training Points
FIFA Soccer 12 Premium Gold Pack
Call of Duty: Black Ops Rezurrection: Content Pack 4
Angry Birds (PlayStation Mini)
FUT - Premium Gold Pack
MLB 10 The Show Road to the Show Training Points
FIFA Soccer 12 Premium Gold Jumbo