Fun With Freeware: MacOSaiX v2.0
Ah yes, this is better than good -- took a few minutes to mess with MacOSaiX and it it really awesome! You can grab it at http://homepage.mac.com/knarf/...
You can select a photo, pick a few keywords and then grab your mosaic tiles from a bunch of different image sources like google images, or flickr, or use glyphs (i haven't tried that yet though).
Here's the MacOSaiX (from my photo) I made this afternoon.