My favorite so far has been the gas cap mod...
Here are a few more threads that are DIY - almost free just require paint and sandpaper:
Custom Badging and De-Badging
http://legacygt.com/forums/showthread.php?t=76676
Painting stock wheels
http://legacygt.com/forums/showthread.php?t=82945
DIY grilles - paint, mesh
http://legacygt.com/forums/showthread.php?t=86186