I’m not entirely sure if Valve are making a statement with their latest Steam sale: today of all days you can now buy cheap Linux games. Titles on offer include Defcon, FTL, Red Orchestra, Amnesia, and World of Goo.
If I was going to pick out a good bargain or three I’d suggest that FTL, and Dungeons and Dredmor between them would keep you playing for a good week or so, for a grand total of under £6.
Note that although the sale is marked as a Linux sale, the games on sale are all playable on Windows, and most are also playable on Mac.
Go, buy. And remember that if you play something this evening, you’ll probably be playing it for months following.
Also: Team Fortress 2 for Linux is available and by playing it, you'll earn a Tux Penguin.