GoodOldGames (GoG) has announced Linux support, and attached a sale to it. Some games are 75% off.
All are Windows and Linux, with some of them working on Mac.
Head out to the promo page and find out which of them you can get up to 75% off until Tuesday, 9:59AM GMT. Of course, all of the games from the list above that you already own will be updated with Linux versions with no additional cost for you, just as you might have expected from GOG.com.
With a lot of GOG games being DOSBox wrappers I have no idea why this didn't happen sooner