although i have to give props to Gamefly for their consistantly good condition, complete games I have purchased from them, Amazons service and fantastic deals never fail to impress.
The majority of my game purchases the last six months have been from Warehouse Deals. I'm currently in the market for another 360 since my last RRoD. Most likely will get it from them as well.
Gamefly. I don't rent from them, but have bought several used games in the past year during their sales, and all of them have included the manuals and any online codes.
Was a toss up here for me between Amazon Warehouse deals and Gamefly. Had a hard time choosing but Amazon since I got in on a few more deals there and missed out on a lot of the Gamefly ones.