I found a website that for a one time, non recurring fee, you can download all the Xbox 360 games for free. The ultimate package is $34.99, which in my opinion is a great price considering the newer Xbox games are $50.00 and up.

They carry all the newest titles, including Halo 3, Halo: ODST, Left 4 dead, GTA IV, and many more. I am proud to be a member. Here is the site, Buy. I'd say that it is worth a look if you are not willing to pay outrageous prices for games. Also, you don't need to do anything technical to your Xbox, it wont void your warranty, and it requires no modifications.