PC Where to find old big box PC games?

[Interinactive]

Tom Clancy games, id games, point and click adventures, old RPGs, anything really. I actually started collecting older games, then I bought a tonne of new ones, and I want to go back to getting the classics I grew up with. And to make it harder for myself I usually only go for the sealed ones.

This is probably my favourite one so far

http://i.imgur.com/1DVptfd.jpg

If there were a store that sold big boxes like that in that sort of condition I'd probably take out a loan, but they are few and far between.