Steam is also throwing a sale for the release of Steam for Linux: http://store.steampowered.com/sale/linux_release/; ends February 21st, 18:00 GMT. Highly acclaimed "Team Fortress 2" is free to play: http://store.steampowered.com/app/440
And Trine 2 is good fun and absolutely beautiful!
(Not associated with either, I just like them...)