Stumpokapow
listen to the mad man
Other weird stuff.
Civ V - Frankenstein
DayZ
Ikari Warriors
TERA (was on Steam then removed)
The Banner Saga: Factions (Kickstarter game)
[CONSOLE] Half-Life 2 Multiplayer
Dota 2 DLC Range
Age of Conan
Anarchy Online
Seven Souls Online
Crysis 2 GOTY
Skullgirls
Runescape
Saints Row IV (wat)
World of Tanks
Some of these seem pretty logical; stuff that's removed from Steam maintains its registry entries, for re-download purposes and so stuff like the box art in the client is kept behind the scenes after the thing is removed.
We know Skullgirls is getting a PC port.