The New York Public Library Digital Gallery contains a wealth of historical art and illustration. Most images are public domain, but the Library does charge a usage fee to license an image for commercial use. A great source of inspiration for patterns and antique designs.
iStockphoto, recently purchased by Getty Images, is an inexpensive source of royalty free stock photography and illustration. Prices range from $1-$15 (as opposed to $400 for a royalty-free image on Getty's site). Let's hope they stay this cheap.
I haven't used these before, but they're worth looking into: Fotolia, Big Stock Photo, and StockXPert.
You have read this article resources with the title Photo and illustration sources. You can bookmark this page URL http://jenkrebs.blogspot.com/2007/01/photo-and-illustration-sources.html. Thanks!