Good Old Games
I'm not a shareholder or anything, but www dot gog dot com lets you easily buy "Good Old Games" including many mentioned in this thread.
The prices are pitifully low and they have all had their copy protection removed, and are all guaranteed to work on modern day operating systems - which alone is worth the price for most of them, as you will know if you've ever tried getting an old game to go in say Windows 7 64bit.
Plus there are great support forums for any bugs that slip through the cracks, and they frequently offer massive discounts that take the prices down into the realms of $1 per game and even free.