An AIGA survey of web, freelance, art director, and graphic design salaries in 2003 (in the U.S.): http://www.aquent.com/WhitePapers/pdfs/AASS_2003.pdf
(via Metafilter)
other interesting surverys/information for designers at: http://marcom.aquent.com/AboutUs/FreeTools/index.html