I got an offer to try Gamefly free for 21 days, so I've been giving it a look. I must say, it's pretty convenient and economical. The cost is $21.95 per month, which is pretty low considering that most games retail for $40-$50. The only two drawback are a) there is no manual (only controller instructions), and b) they don't carry PC games. Surprisingly, they DO carry GBA games.
So far I've rented four games, and I'm still working on two of them. Here are my capsule reviews. BloodRayne (XBox version): bad. Otogi: Myth of Demons (XBox version): OK. Freedom
Fighters (XBox version): great. Viewtiful Joe: great.
I'm also playing Battlefield: 1942, which is still a blast a year later. If you like multiplayer PC games, I wholeheartedly recommend buying it and the latest expansion. Good fun.