It's probably a mistake, but right now Penumbra: Black Plague Gold Edition is $0.75 at GamersGate: http://www.gamersgate.com/DD-PENBPG/penumbra-black-plague-gold-edition-bundle
Too bad Black Plague uses SecuRom, but if you don't mind, there you go.
That's a damn good deal... too bad I already own the Penumbra Collection ;).
Osmos is on sale for £1.99 on GG: http://www.gamersgate.co.uk/DDB-OSMOS/osmos-bundle?caff=2060361
The entire Penumbra Collection (three games) is on sale for £4.50 on GG: http://www.gamersgate.co.uk/DDB-PC/penumbra-collection-bundle?caff=2060361
Machinarium is on sale for £3.75 on GG: http://www.gamersgate.co.uk/DDB-MACHIN/machinarium-bundle?caff=2060361
Space Pirates and Zombies is on sale for £3.48 on GG: http://www.gamersgate.co.uk/DD-SPAZ/space-pirates-and-zombies?caff=2060361
Puzzle Bots is on sale for £1.75 on GG: http://www.gamersgate.co.uk/DD-PBOTS/puzzle-bots?caff=2060361
Wizorb is on sale for £1.67 on GG: http://www.gamersgate.co.uk/DD-WIZORB/wizorb?caff=2060361
Cthulhu Saves the World is on sale for £1.00 on GG individually and for £2.99 as a 4-pack (in case you have friends who want to pitch in): http://www.gamersgate.co.uk/DD-CSW/cthulhu-saves-the-world?caff=2060361 http://www.gamersgate.co.uk/DDB-CSW4P/cthulhu-saves-the-world-4-pack-bundle?caff=2060361
Whew... I hope these haven't been posted yet.
I can personally recommend Wizorb, Machinarium, Puzzle Bots, the Penumbra Collection and Cthulhu Saves the World. I've played them all and they're great games despite being relatively unknown to some.
Wizorb is a JRPG/Break-Out hybrid - a fun way to waste time and quite original.
Machinarium and Puzzle Bots are both great adventure/puzzle games.
The Penumbra Collection includes three horror games from the makers of Amnesia: The Dark Descent and is truly terrifying (if you're into that sort of thing).
And Cthulhu Saves the World is a really funny twist on the JRPG genre and well worth a play to all of those among you who like JRPGs but are sick of the usual tropes (or anyone who wants to play an original, comedic JRPG).