Saw this on Steam's website a couple of days ago. Not the first time it's gone down to $5 but nevertheless, still a pretty good deal. Get it, hook your comp up to a 50-inch tv, and sit five feet away.
Bioshock - http://store.steampowered.com/app/7670/
Bioshock 2 - http://store.steampowered.com/app/8850/
EDIT: the $4.99 price tag for Bioshock 2 is US ONLY. AU's price is $12.49. Bioshock still remains at $4.99.
Windows only.
EVOLVE TODAY!
It's incredible such a good game was destroyed by its sequel that was more like an expansion than anything else. This franchise had real potential, interesting graphics, storyline and weapons.
Good price though!