Resistance 3 has a stellar single player. I haven't played much of the multiplayer but what I have played is fun for both buddies on the couch and online. My brother played it literally all weekend. Unfortunately, the original Resistance is just OK and the second one barely scrapes the surface of OK, what with all the balance issues and the refilling health/two weapon limit the second one had. Never fear, the third doesn't have those problems at all!
Uncharted 2 has some of the best writing this side of Bioware and its levels and gameplay aren't bad to boot, though I have to admit that it never struck me as the "best action adventure game EVAR" that so many reviewers placed on it upon release. Like Resistance 3, its multiplayer is really good. People still play it.
The God of War collection packs two of the best action games I've ever played, and while my action game resume isn't as long as I'd like it to be the games are still great. The Origins collection, even though it was on the PSP, translates to the PS3 perfectly and Ghost of Sparta somehow looks better and clearer than God of War 2 did on the PS3.
InFamous is a pretty fun to play open-world game.
If you're in for something colorful and don't mind something that kids could play without anybody worrying, pick up the two Ratchet games on PS3. Not only are they gorgeous, they're also incredibly fun.
There will be a Jak and Daxter HD Collection coming soon. Unlike the other games on this list, this particular one is a NECESSITY. You must get it if you own or have access to a PS3. And if you have a PS2, you must get the first three.