I found it difficult to find any good information on the subject so this book page will serve as one thread to rule them all by region. If you have any info to add just click on edit at the top of the page.

Links are organized by location of distribution centers.

Overview of all the major players.

All of the US
Gamerang

US East coast

US West Coast
Gamefly problems?
Gamefly?
GameFly "Fast Return"?
GameFly users?
WTF is up with GameFly

US Cream filling

Canada
Game Access

Other locations