GOG has all King's Quest, Space Quest, and Police Quest games 50% off this weekend.
Alas, due to ridiculous regional pricing, Space Marine is still US $30.59 for me, even with 66% off.
New Indie gala!
Pay $1-$4 and you will get 3 games, pay $4-$7 and you will get 5 games, pay more and you will get the last Gala bundle as well. Not a whole lot of money for a whole lot of games.
*edit* Paypal is clogged, so don't expect to get your keys right away.
I don't get why this indie gala thing bundles a bunch of music along with the games. I know they say there's some intrinsic link between games and music, but honestly I don't see it. I may be willing to take a chance on some puzzle game and not feel ripped off if I don't like it, but I know in advance that some indie rock hipster crap is going to be a total waste. Now an indie metal bundle? I'd be there, as long as it's not bundled with a bunch of insipid clones of the latest iphone timewasters.
The games offered this time include a fantastical first-person action-adventure game (Steam for PC), an IGF-nominated puzzle adventure title (Steam for PC and Mac, Desura for PC and Linux, DRM-free PC, Mac and Linux download), a 'scorching' single and multiplayer arcade-strategy game (Steam for PC and Mac), and a world premiere on PC for a pair of retro RPG-defense games (Desura for PC, DRM-free PC download).
Two Worlds: Epic Edition is 50% off on GOG through the weekend - so its $5. I've never played it so I don't know how good it is but might be worth a try for that price.