Viget Inspire

• istockphoto.com - giant selection of royalty-free stock images and photos
• gettyimages.com - the leading provider of creative and editorial imagery and film to communications
• moodboard.com - buy or sell images at a range of prices to suit your needs
• jupiterimages.com - offers anything from royalty-free DVD collections to standard rights-managed images and royalty-free images
• digitalrailroad.net - selection of royalty-free and rights- managed stock shots, but it also features an eBay-like marketplace where photographers vie to meet your requirements by the deadline

Inexpensive Alternatives

• fotolia.com - inexpensive stock photography, photographers can also sign up to sell stock photos
• dreamstime.com - essentially a royalty-free microstock site, the selection is limited
• ultrashock.com - offers high-res photos, conceptual vector illustration and other assets

Specialty Providers

• foodanddrinkphotos.com - a comprehensive collection of photos about eating and drinking
• sciencephoto.com - features some of the best science related stock photos available online

Freebies

• photolib.noaa.gov - one example of the many photos you can use for free from U.S. Government sites.
• public-domain-photos.com - claims to be the largest collection of public domain photos
• sxc.hu - the leading free stock photo site
• morguefile.com - contains photographs freely contributed by many artists to be used in creative projects by visitors to the site
• stockvault.net - a stock photo sharing website where designers and photographers can meet to share their images
• freerangestock.com - high-resolution free stock photos and free textures
• photogen.com - nice collection of good quality photos
• flickr.com - best online photo management and sharing application; be sure to check the license before using any of the photos
• everystockphoto.com - excellent option for searching multiple sites (Flickr, Stock.xchng, etc.) for stock photos

Feel free to add sites that been left out!