Simply put... Any you can actually walk into and ask a real person!
This kind of electronics, certainly in the UK anyway, must be disposed of in the proper manner. This means conforming to Health and Safety W.E.E. Regulations, and storing, "Waste Electrical and Electronics", until an official body can come and remove it. Often for a cost! This means, again in the UK, that many small PC repair shops are very happy to palm off what is useless to them and can offset some nominal cost.
I know Health and Safety may not be as harsh in the US but I feel sure that environmental regulations must exist, even if they may not adhered to.
Know what you're after, (16x DVD rewriters, whatever, it shows you know what you want), and be bold, walk right up to the guy and ask him. If you get one working and want another one, take your creation with you and show them. What's the worst that can happen? That's right, he says no!
Don't get carried away though, you'll fill your garage with junk in no time that way!
(Although on return visits in my early days, and after burning the guy's desk on request, I've been given HDDs, mini HDDs, laptop heatsinks, etc... All cool stuff to rip into.)
Happy hunting...
M
