I too have this problem.
Midnight, Mutants & Masterminds, d20 Modern, the Core books, Conan, Iron Kingdoms, Call of Cthulhu, Mekton, Heavy Gear, Scarred Lands, Forgotten Realms, and a slew of other stuff. Stuff I wouldn't use. Stuff I >gasp< decided to sell. I kept/keeping about half my...