I'll just list off a bunch of my favorite games:
Anything made by Insomniac: Seriously, these guys are on fire. Three R&C games, and two Resistance games, and I love every one of them. My collection would be much less impressive without these games. Plus, if you track down a BC PS3, get the PS2 Ratchets too. Even Deadlocked. That's right, even Deadlocked.
Heavenly Sword is a fantastic game. If you can find it for cheap, go for it. Very good game, and Andy Serkis as King Bohan is awesome.
inFamous is another great one. If you're into the open world type games, this is definitely a great one to get. The powers are plenty of fun to use (though I wouldn't say no to more of them), and the story, while interesting enough in the beginning, takes a huge twist once you get to the third island. Definitely one of my all time favorite games.
LBP goes without saying, really. The story levels are good, but after that, you still have tons of other levels to play. Some are great, some are funny... some are unintentionally funny. There's all kinds of cool stuff to see in the game. Plus, I have tons of fun making a "level" with friends. Basically, just messing around with the editor. Building levels can be fun too. Especially when things actually work the way they're supposed to.
I would highly recommend Warhawk as well, but I'm afraid it's probably a bit late for people to start playing the game now. I haven't been able to get my PS3 online much in a while, but everything I've heard says there's still an active community. It's just that if you're a new player, you're gonna die. A lot. A whole lot. Maybe wait for Starhawk, which had better be announced soon or I will explode.
These games are multiplat, but I still love them.
Assassin's Creed I and II. Yes, I love the first one. Sure, the gameplay was repetitive, but I found the game very interesting, and honestly, the view points made my jaw drop a few times. They are good in ACII, but not nearly as good as in the first. I have to admit though, that ACII is better in virtually every other way. 
SW: The Force Unleashed. Yeah, more repetitive and whatnot. But I loved it. It's a blast. While there aren't nearly enough, the force powers do feel pretty awesome to use. Plus, I feel like such a badass crushing chicken walkers left and right. Sadly, the level where you take down the star destroyer is horribly done, and incredibly frustrating. But the game for the most part is very interesting and quite enjoyable.
I'm sure that many people will disagree with me on some of this stuff. But in my opinion, these are all great games.
