I've been renting them from Blockbuster to find out which ones I like. They are 5 day rentals and you get a 7 day grace period with no late fees at all, so you can keep it for 12 days. If I like a game, I'll buy it. Saves money, and your progress from renting it is saved on the console. So far, I haven't played anything online.
Resistance: Fall of Man is cool. I ended up buying it after I rented it. It's badass to play split screen in co-op mode. My roommate and I beat it on easy, and recently found out that medium is ridiculously more difficult.
COD4 is very, very badass. Again, I haven't even played this online. It's fairly easy to beat on the easy mode. This is the coolest game I have played so far. I really wish it had a split screen co-op mode. Definitely buy this game.
Time Crisis 4 is a lot of fun. It's fast paced and using the gun makes for a more interactive experience. It will wear you out a lot faster though, so in a way it gets old if you try to play it straight through. You have to hang sensors from the top of your TV, which is kinda lame. Also, the gun is corded (why not Bluetooth?!?!?) and the cord is not very long at all. Maybe 10-12 feet. The biggest down side to this game is that you cannot buy a second gun separately. I think it would be kickass in 2 player mode, but I am having trouble justifying the purchase of another $80 game setup just to get another gun. The game is cool enough to warrant $80, but not $160. Supposedly there will be stand-alone guns available eventually.
I rented Assasin's Creed, and couldn't get into it. The storyline is too slow, and you can't skip through the bs between the action. The majority of the game is spent walking around, reminding me almost of Zelda, which I hated. The controller setup is much more complicated than it needs to be. The fighting is plain. The graphics are really cool, though. Maybe it gets better when you get deeper into the game, but I lost interest after the first hour or two.
I got Lair as a Christmas gift. I'm into dragons, and the game seems like it will be really badass. I just haven't really played it much at all. It relies heavily on use of the six-axis fucntion of the controller, which will take some getting used to. The very little bit I've played it seemed cool, I just haven't invested much time into it. I can see it being a game where you either love it or hate it.
I am currently playing Need For Speed Carbon, and I like it. It's worth buying. Cool game, and not so realistic to the point where it's really hard to drive. I was able to start winning races immediately. You could spend forever playing this game, even after you complete a career. My only gripe is that it always takes place at night. I found myself wanting a change of pace in the form of a daylight race.
I also have NBA 07. I picked it up really cheap (like $15), and still wasted my money. The instruction manual is useless, and doesn't explain half of the functions of the game. I could not find a tutorial in the game itself. having not played the 06 or any earlier versions, I didn't know what was going on and couldn't make shots for shit. Very frustrating, and just not worth the trouble. I have yet to try another b-ball game, but I'm sure there are better ones.
Same for Tiger Woods golf. I rented that game and took it back the next day. I've never golfed, so all of the terms and choices were completely foreign to me. If you have a clue about golf, you'd probably do fine. I could see it being a challenge and very enjoyable for golf enthusiasts.
Cars Maternational - only cool if you are under the age of 6. Why did I rent this game?
I think those are the only ones I've tried so far. if I think of any I missed, I will post up again.