fileinfo.com: Image File Formats
Image file extensions and their associated file formats.
martinreddy.net: The Graphics File Format Page
Contains specifications for various graphics file formats; along with a number of relevant graphics utilities, information, and URLs.
w3.org: Web Graphics
Overview of graphics formats for the Web from W3C. Includes links to descriptions of SVG, WebCGM, PNG, JPEG and GIF, plus how to integrate images in XML and HTML pages
Add Site or Add URL to Submit Site to the Graphics Directory