Batman: Arkham Asylum: A really good mix of stealth and action. They do a good job of capturing the "badass" element of Batman, and the production values are very high. Except for tracking down riddles and challenge mode, which basically presents certain set pieces from the main game with new/harder objectives, there isn't much replay. It can get a little repetitive, but if you're a Batman fan, or if you like stealth action games, you should give it a try.
Red Faction Guerrilla:I rented Red Faction games before to multiplay with friends when we were bored, but I never got into them enough to get involved in the single player campaign. I tried a demo of Guerrilla though, and got hooked. You can destroy almost anything (aside from huge rocks and the planet of Mars itself) that you can see. If you come up with some wild strategy for a mission, chances are you can do it. For a hostage rescue, lets say you take out enemy snipers though the walls with a rail gun from far off, then ram through the building with a big truck. After getting the hostages into the truck, just drive out the other wall - or blow it up first, and high tail it to safety. There is also a mission where they change the entire feeling of the game for one area. One of the best "open world" games I've played in a long time.
Prototype: You'll either love this one or hate it. If running around like a lunatic, vaulting over buildings, flying, shapeshifting, elbow dropping tanks and slicing through man and beast alike with whip and/or blade arms is your cup of tea, welcome to the party.
If you like Prototype, you might also want to give Crackdown and Spider-man:Web of Shadows a try. A lot of these I would consider better rentals than purchases, but they'll still a fun ride while they last.
Vagrancy - Be careful who you wake up in a twenty four hour parking lot.
His name was Not Johnny - A young man becomes a sort of superhero after a crippling injury. He