Why limit yourself to new games?
I primarily game on my 360, so most games I buy get bought for that. I don't have many PS3 games and the ones I do have don't have local co-op or multiplayer. But I love to play games with someone in the same room.
So recently, I've been buying older games to play with my buddy. I picked up Gauntlet Legends for PSone for about $5 shipped on eBay and we have been having a blast playing that. Brings back so many memories from being a young'n and playing the game at Fudruckers or the mall.
I'll second the Lego games as well. They are so much fun, single-player or co-op.