STALKER: Call of Pripyat is available on Steam for $20 if you already own Steam copies of either Shadow of Chernobyl or Clear Sky.
If you don't own a copy of Shadow of Chernobyl or Clear Sky but want Pripyat you can just buy Clear Sky and then take the discount on Call of Pripyat, either way comes out to be $30 and that way you get one extra game.
I'm assuming they don't check for the date you bought it, and it's just that you own them.
Is Mount&blade any good? I've seen good reviews online,but a $5 game that isn't even 2 years old yet looks fishy..which reminds me of my purchase of Two Worlds. D:!
I don't know about Mount and Blade specifically, but I've made $5-$10 game purchases that I have been much happier with than some $50 games.