Lots of stuff, but I'm happiest about Winterbottom, the Quake pack (original, not crappy Quake 2), Gratuitous Space Battles and Aquaria.
Worst purchase: Gish. That game is awful. It's harder than Super Meat Boy and controls way worse. Don't get it.
Worst purchase: Gish. That game is awful. It's harder than Super Meat Boy and controls way worse. Don't get it.