GOG End of the World sale has some cracking deals
Witcher 2 $7.50, FTL $5, etc. and then there's the bundles.
I suppose offering games for pittance makes sense if your sale only lasts a day. That's what Good old Games is doing. It's an End of the World sale and it ends 22 hours from now (5pm UK time).
The biggest deal is The Witcher 2 for $7.49, but there's also FTL for $5, Witcher 1 for $2.49 and Fahrenheit for $3.
There are loads and loads more, like all the old role-playing greats Planescape: Torment, Icewind Dale and Fallout all $5 each. Even Far Cry 2 and Psychonauts are $5. It goes on and on and on.
Generally most money is saved on GOG game bundles. There's a great indie bundle that includes Stacking and Machinarium and To The Moon and others for $20. There's a Bullfrog golden oldies bundle with Populous 1-3, Dungeon Keeper 1 & 2, Syndicate, Theme Hospital and Magic Carpet for $11.92.