as a note to everyone who has mentioned deus ex and it's sequel, they are still available - on steam.
(not sure if mentioning them gets a lad stoned here or what, but they sell them. its where i bought mine after a particularly nasty house-move that lost many, many cd-roms in it's process.)
Lot's of games here are still on sale elsewhere. All the X-Com games have just been made available on Steam for example. Every time we find out a game is available elsewhere we know two things: 1) it will cost us more than $5.99 and 2) We will be expected to do all the legwork to get the game to work on our modern PC's!
If a game isn't available elsewhere we can only hope that G.O.G gets it first - it'll be cheaper and easier for us that way!! :)