Uncharted: Drake's Fortune
Absolutely excellent 3rd person action adventure. Kind of Tomb Raider-esque (lost treasure, etc.), but with more action (& a very Gears-like cover system). One of the best looking, & best playing, exclusives on the PS3. Story, graphics, sound, voice acting, gameplay... all top notch. It's also on budget now so is very cheap
Metal Gear Solid 4
Awesome physics-based platformer, hiding behind a cutesy exterior. Great single player, great multiplayer, & a comprehensive level creation mode.
3rd person hack & slash. Gorgeous graphics, great story, good action. Not overly long, but I still loved it. Much preferred it to Devil May Cry 4 (too boring!), & Ninja Gaiden (too frustrating!
). On budget, so very cheap.
Also consider Resistance 1 & 2... although they're not up to the standard of Gears/Halo IMO, they're still both pretty good shooters. No. 1 is on budget, no.2 came out last week.
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Oh, & once you've got it hooked up to the 'net & got your PSN account sorted...
1) Shove your PSN ID here
2) Get on the PSN Store (equivalent to the XBL Marketplace), & try out some of the games. Super Stardust HD & Riff: Everyday Shooter are both excellent, & very cheap. Also well worth getting is Wipeout HD - at around 12 quid it's a bit more than the cheaper games like SS HD, but it's brilliant.