toptenreviews.com does extensive research on this topic this year and did review of all top service providers in multiple categories and compares them. Gamerang.com got rated the highest. The only other one I was considering was Gamefly.com but I don't like the website design and content as much.

They mailed my game on Jul 31 and I got it on Aug 1. So far it's great. The price is not too high, it seems normal enough. I read the reviews...
Online Video Game Rental Review 2007

Check that out.