Dungeons 2 - Free, for the next day or so via Humble Store
I used to love Dungeon Keeper, and this seems to be some sort of remake. Not sure why it's free (probably a sequel soon), but hey, a decent price
PS With these sort of free deals on Humble Store, you have about 10 days or so to redeem the Steam key, otherwise it expires it. A new 'stop hoarding/reselling' thing I think.