This thread is to keep Steam Card discussions out of the Steam Sales thread.

I'll start off with some games which you can effectively get for free or make a [very] small profit on. Thanks goes to Big Z for pointing these out.

Cherry Tree High Comedy Club and Ether Vapor Remaster can be picked up from http://groupees.com/doujin for the next day and a half for $1.50 for the pair.

Cherry Tree has 10 cards, so you'll drop 5. Those five cards are selling for $0.25-0.40ea.

Ether Vapor has 6 cards, so you'll drop 3. Those three cards are selling for $0.17-0.20ea.

Conservatively, assuming no foils and the lowest value cards, you'll still rake in [[5 x 0.25] + [3 x 0.17]] / 1.15 = $1.53, which was the combined purchase price of the two games anyway. Of course, you're very likely to get higher value cards than the unfortunate selection I based the calc on, and you'll have two new games in your library too.

edit: If you're hunting badges, then the Groupee deal has depressed the card market, so it's very cheap to buy a badge at the moment. Selling the Cherry Tree cards would give you more than enough for an Ether Vapor badge. The card market for these two games might bounce back after the Groupee deal closes and the card glut has passed.