http://http://www.certifit.com/
I am a 4wd fanatic that has recently bought into a Subaru.
the site above has hundreds of car parts for cheap. The are not OEM
but the parts are good quality. I have purchased fenders, a hood, and many tail lights from them.
(edit:)
depending on the model Impreza
Fender's run 24.95-40.95
hoods run 78-102
the signal lamp assy will be 16.25-22.04
I don't have a list for the head lamp though.
It's nice to have a parts book:D