I just wrote a nice AppleScript, Switch Icon, that uses images.google.com to cycle the iChat buddy icon through 20 selected images. Start iChat, then start the "Switch Icon" script and reply to the dialog asking if you have GraphicConverter installed (for nice cropping). Then enter an initial search string (i.e. red porsche or Mac G5, etc.) and it will start cycling a new icon every 10 seconds.
The second script, "Switch Icon Query", is a two-liner that can be placed into the script menu and will just reset the query string to something different.
If anybody knows how to crop JPEG images from AppleScript with its built-in tools, please let me know. The main script is only tested with iChat AV - not sure if it works with iChat 1.0 or not.
[robg adds: The Switch Icon script is somewhat long, so rather than attempt to format it for display in Geeklog, I just put both files online in a stuffed archive: switch_icons.sit [42kb download]. I've tested the script, and it works as described. If you think 10 seconds is too often (not often enough) to change your iChat icon, just edit the second to last line in the script -- the line that reads return 10 is the delay line, and 10 is the delay in seconds.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030802210512820