Haven't had much luck on the physical side, but on the digital...
GOG:
The Dark Eye: Chains of Satinav - free GOG key from a developer giveaway at Reddit.
Steam:
Alpha Prime - from the Bohemia Interactive Humble Weekly. Free from a friend.
Star Wars: Empire at War - traded some TF2 items for this.
Teleglitch + Guns n' Tunes DLC + some soundtracks (Humble Roguelike Weekly) - $3ish after selling off my dupes
Castle of Illusion - $4 after getting a discount on a sale at GamersGate
Gravity Badgers + Ballpoint Universe: Infinite + Deadly Premonition: The Director's Cut + Viscera Cleanup Detail: Santa's Rampage - $2, yay Indie Gala
Sanctum 2 Season Pass + DLC Skin Pack - $2.20ish
Star Wars: Jedi Knight Collection (Jedi Knight II: Jedi Outcast, Jedi Knight: Dark Forces II, Jedi Knight: Jedi Academy, Jedi Knight: Mysteries of the Sith, Star Wars: Dark Forces) - $5. This is still in my inventory.
I also traded away that duplicate Deadpool copy I got because GameFly sucks, and so I got 10 TF2 keys, which I've been using to get other games that are sitting in my inventory:
Hitman: Absolution Professional Edition
Star Wars: Knights of the Old Republic II
Ninja Blade
Edit: Oh, right! I forgot. I got The War in Heaven, some weird Christian FPS thing, for two bucks a little while back. Still new.