Most of these games have been bundled, highly discounted, or even free at some point. 

100% Orange Juice
99 Spirits
Akane the Kunoichi 
Alien Rage: Unlimited
Alternativa
Awesomenauts
Batman: Arkham Origins
Blackbay Asylum
Blade Symphony
Bleed
Brothers: A Tale of Two Sons
Cargo Commander
Claire
Clive Barker's Jericho
Cloud Chamber
Collapse
Contagion
Contraption Maker
Crysis
Dead Island GOTY
Deadly Premonition: The Director's Cut
Defense Grid
Deponia: The Complete Journey
Disciples III: Reincarnation
Disciples III: Renaissance
Disciples III: Resurrection
Divinity II: The Developer's Cut
Doorways
Dragon Age Origins: Ultimate Edition (Not available for purchase in my region)
Dungeon Defenders + DLC (Humble)
Edna & Harvey: Harvey's New Eyes
Edna & Harvey: The Breakout
Faerie Solitaire
Fallout: New Vegas
Far Cry 1, 2, 3, Blood Dragon
Fate: The Traitor Soul
Game of Thrones
Glare
Gothic Universe Edition
Guilty Gear Isuka
Hack Slash Loot
Hotline Miami
How to Survive
Interstellar Marines - Spearhead Edition
Joe Danger 1 & 2
Kairo
King's Bounty: Warriors of the North
Max Payne 3
Motte Island
Mount & Blade: Warband
Painkiller Black Edition
Painkiller Overdose
Painkiller Redemption
Papers, Please
Paranautical Activity
Psychonauts
Realms of Arkania Complete Classic Trilogy
Red Faction: Armageddon
Rust
Shadowgrounds: Survivor
Shank
Sid Meier's Civilization V
Slender: The Arrival
Sniper Elite: Nazi Zombie Army 1 & 2
Sniper: Ghost Warrior 1 & 2
Still Life 1 & 2
Takedown: Red Sabre (key only)
The Walking Dead Season 1 & 2
Thief 2014
Thief II: The Metal Age
Thief: Deadly Shadows
Torchlight
Tower Wars
Tryst
Two Brothers
Violett
War of the Human Tanks