I've frequently commented in the past on the Game Developers Salary Survey. For you Pythonistas out there, there's some nice data (amateur grade, but still pretty good) to be found at the Python Developer Salary Survey. No mention of what you get for knowing Max / Maya, however, but by crunching the numbers I'd guess it subtracts about $30k per year.
Or maybe that's just because we're all lousy programmers.
EDIT: fixed bad link