I need it for some realtime video processing (head/finger tracking with OpenCV, TouchLib, tBeta...), could spend up to about 150$... True 640x480 would be of course better.
I've read of some webcams (even low cost ones) that support 640x480@60fps, like Phillips SPC900-NC, Sony PlayStation3 Eye or Logitech QuickCam Pro 9000, but I'm not sure on how they're working on Linux...