While it's not free, $20 ain't bad.
While building my HTPC, I used techbargains.com to locate a DVD burner for $49 and an 802.11b USB adapter for $0.
It looks like this guy makes his money by setting up referrer accounts with the retailers. The link above uses a "jump" from his site. I presume that this logs the referral from his site TO the retailer's site and he gets some kind of cut from them. Who cares? We get the low price without having to crawl all over the web or get our fingers black from flipping through all those newspaper flyers!