Yesterday my iPod crashed while I was listening to a Sigur Rós album
Normally when that happens (not necessarily while listening to Sigur Rós!) I hold the menu and enter buttons down for 5-10 seconds and it reboots, but this time that didn’t work
I did a google search and found a forum post on macrumors.com that worked a charm:

– Plug the iPod into the power charger ONLY and not the computer
– Toggle the hold switch to on and then off
– Hold the MENU and Select (center) portion of the wheel down simultaneously for ten seconds.

It means you need to have a mains charger which you don’t get out of the box when you buy a new iPod
I was about to get the putty knife out and pull the battery out to reboot it, which am glad I didn’t have to do