Well Roy I know what I've played and like, in random order.
Tony Hawk Pro Skater - whichever one. great games but you really have to stick with them and play them lots, very skillful game to master. assuming you're getting 12 it may not be the best option.
Call of Duty 4 - insane. online it's masterful, campaign it's a blast. remember, when you get to the ferris wheel lay down in the prone on the other side of the stage and shoot under the stage and through the fence, that'll save you hrs of game play on the harder levels.
Top Spin 3 - don't be deterred by tennis games of the past, 2 was a great game and 3's highly touted with online support.
OBLIVION - the only problem with this game is as adults we have too much money to stick with one game. if i was going to go back to childhood and have one game to take with me this would be it. it's infinite, think back to your Final Fantasy/Zelda days, that's how I felt playing this game. but wow it takes up a lot of your time. second highest game rating of all time other than GTA IV.
Star Wars the Force Unleashed - obviously it's out in Sept which is a ways away but you're Darth Vader's flippin' apprentice, no need to elaborate on how money that is.
Assassin's Creed - the first game to somewhat fully harness the capabilities of the system. aside from being stunning, it's a blast to play.
Star Wars Lego - fantastic game. i play it with my 4 year old niece and we both have a blast. i know it sounds rediculous and i was the first kind of person to scoff at it but it's so much fun. great when you're drinking or on the phone, or on Celticsblog
The Orange Box - it's Half-Life 2, Portal, and Team Fortress 2 all bundled up into one game. Half Life 2 is to me the best made video game of all time, just not long enough. i can only assume you've seen it on pc though.
Splinter Cell - if you haven't played the Splinter Cell series much buy them all and start with the oldest one and work your way up. masterful games, terrific system and each one is far better than the last. very replayable too, getting through each level without being detected once is quite a chore.
Table Tennis - Mario Kart type fun.
Pretty much it for me Roy, not too swept up some of the more obscure titles these days, I stick to my EA games exclusively these days for the most part. Some of these titles are for both systems but I don't pay attention to PS3.