Good Old Games is now selling the PC version of the Most Excellent Game Psychonauts for a measly $9.99 (or £6). The game was Double Fine's first release, directed by Tim Schafer and written by Tim and Erik Wolpaw, Old Man Murray co-writer and future writer of Portal (their future, not ours).
Although, in order to maximize Double Fine money, you should try buying it from the Double Fine Shop, which is also selling signed copies of Brutal Legend.
Finally, I wanted to point you to this excellent interview Tim did with Tom Chick. I've linked to it before, and I'll link to it again: although, do beware of spoilers, since there's plenty of them even before the all-caps SPOILERS tag. I think I'll start doing something like that, now, when I put the warning labels on the inside of the pills bottles in my drug rehab volunteer work. Thanks, guys.