Optimizing Images for the Web

There is a comprehensive article we're passing around at work today:
http://webmonkey.wired.com/webmonkey/98/26/index0a_page3.html?tw=design
It explains the differences between gif, jpg and the enigmatic png formats, then goes on to lots of technical specifics like changing bit depth to save file size, etc. Very helpful if you work with the web, though you likely know a lot of it already.
In general, Webmonkey is a great site and resource for working with the web.