Yeah, I hear ya. If you haven't played Fallout 3 yet, then I would say definitely give it a go... the sad thing is that it's actually a better port on the 360 and PC, but whatever... it's certainly more than passable on the PS3.
Is your system backwards compatible? I'm confused where Sony is on that whole mess. For a while they were doing it with all systems, then they stopped, then they started up again with the Metal Gear systems and now... well, I dunno where they are. If yours has backwards compatibility, I would definitely recommend both God of War games. They are incredible, even for PS2 games and they're super cheap... $10 or $15.
My favorite games so far have probably been some of the arcade titles. Pixeljunk Monsters and Eden are both pretty fun. I LOVED Puzzle Quest and played that for hours. There's lots of good stuff in the arcade if you're looking to spend $10 or $15 instead of going out and dropping $60 on a bigger title.
Little Big Planet is fantastic... just a fun game. Your kids would probably like that one too, depending how old they are. You can design your own boards and stuff. It's like half Mario Brothers and half erector set.
Killzone 2 is a must have if you're into first person shooters. It's loads of fun, incredibly violent and packed to the gills with action. There's no other game like it on the system.
Motorstorm is a pretty great too. It's a very fast, very fun, very muddy arcade racer. I only have the first one, but it's got incredible graphics and I'm told the sequel is even better.
Beyond that, I dunno... Resident Evil 5 looks fantastic and is fun once you get into it, but it has a few frustrating quirks that tended to ruin my experience with it (you can't shoot while running, so when you try to kill people you stand still... shit like that). Farcry 2 is fun to a certain point and then you'll get sick of it... but maybe it's a bargain bin title by now.
If I can think of any others, I'll put them up.
