I'll second co-optimus. That site is great, and almost always answers my questions about "what kind of co-op does this have"? Game boxes are often intentionally misleading...quoting a two-player mode on a game that should hav obvious co-op...only to be some crappy arena mode.
Here are the list of PS3 games with local co-op that I own and have enjoyed. I'm cheap, but I also only spend my allowance on games...
Shooters (some of these have language):
Army of Two
Campaign was fun, this game is designed for co-op. Also online co-op.
Army of Two 40th day
Campaign was fun, although I didn't like as much as first. 4-player Extraction mode wasn't as fun as I hoped it'd be. Gun custimization was fun.
Conflict: Denied Ops
Another shooter designed around co-op. Not great, but not bad.
Resistance: Fall of Man
Campaign co-op; this game is simply great. The demo of this is what got my wife into shooters. The game has a great story with interesting dialogue in between...it's both interesting and very well done, which is what drew in Brittany. We now regularly play shooters together...often times with her bringing one home. Thank you Insomniac Games! (Thanks for Ratchet & Clank, too!)
Resistance 2
No split screen campaign
However, there is a special co-op mode designed around how an MMO works...3 classes (Soldier/Medic/Marksman). Each class depends on each other. This isn't a throw-together mode, it's really the meat of the game if you're not into PvP...and Britt and I played this online for a very long time. 2 on console split screen with a max team size of 8.
Platformers
Little Big Planet
What can I say, this game is magical. The opening sequence really brought back a sense of awe/wonder I hadn't had for a game since being a kid. Physics are kind of wonky/annoying at times, but the game is a blast for up to 4 players local (or any combination of local/online). TONS of incredible custom levels online...can't be stressed enough.
Hack 'n Slash/Brawler
Sacred 2
Not a great/deep story really, but it does what it needs to do. Can be played local or online, world is huge, lots of loot to find. Outfits can be skimpy on female toons, but nothing too obscene. Best easter egg in the game after a long quest chain...love this song:
http://www.youtube.com/watch?v=5fakNlghOJY
TMNT: Turtles in Time Re-Shelled:
Decent fun, although I would've rather seen them remake some of the other games like TMNT 2 or manhatten project. Hopefully they will. Still a blast with 4 people...total mayhem
Shoot'em'up
1942: Joint Strike (PSN)
Very fun if you liked the arcade game
Gunstar Heroes (PSN)
Very fun if you played and liked the original.
Racing
Modnation Racers
No co-op, per se, but you can race split screen against the computer and split-screen online. Excellent game that takes LBP's "Play. Create. Share" mentality.
Strategy
Pixel Junk Monsters (PSN)
Great tower defense; two players adds to the fun. Has an expansion with a second island.
Misc.
Guitar Hero 3, Guitar Hero World Tour, Rock Band - very fun if you like that sort of thing, which I do
Sonic's Ultimate Genesis Collection - Great if you have someone who remembers these games to play with. Worth the price for the Phantasy Star/Shining Force series alone, though those don't have any real co-op.
Co-op games I've bought on sale but haven't played much yet:
Marvel Ultimate Alliance 2 - Decent brawler/hack'n'slash, not fantastic
Lego Indiana Jones 2: The Adventure Continues - Fun with the kids or even alone, will be fun for a few hours like most lego games, very casual
Lego Star Wars: The Complete Saga - Same as above.
Lord of the Rings- Conquest - Decent game from what I can tell, not great but fun enough for some couch co-op.
Rainbow Six Vegas 2 - I hear this game is simply awesome, and Britt and I will play and love it; just haven't gotten to it yet.
Untold Legends: Dark Kingdom - Decent hack'n'slash
Soldner-X 1&2: Futuristic schmups, fun from the little I've played
Trine (PSN) - More of a puzzler, very fun and interesting. Have heard that wears off
Games I know have co-op, will love to play, just haven't bought due to price (I'm cheap) or massive backlog:
Borderlands - heard the co-op was great
Resident Evil 5 - Now with playstation move support announced
Deadspace Extraction (PSN) - Also move support, on rails shooter game, will be free with Deadspace 2 when these come out
I may have missed some, so I could always go back and look when I get home. Pretty much any of these (as well as ones I haven't listed but own) can be played online...so if you are ever up for that, let me know. Also I'd be happy to give more in-depth on any of these. Anything I missed that I should add?
