Just thought I'd mention that I recently got one of these and am very happy with it. Feel free to ask any questions if you are considering purchasing one. I tried the iPod and the Archos 504 first but the 404 is my favorite. The iPod was sexy, but the DRM was just too constricting.
The 404 has good codec support and the device itself is pretty well designed. Archos also publishes most of the source code for the x04 series of devices so I hope to see some cool firmware hacks in the future.