If you've upgraded your old 60GB/80GB Apple iPod video (5G) or newer iPod classic for Apple's new iPod classic then you should try it in your old case before going out to buy a new one.
While it is thinner than previous iPods (those with hard drives, not the nano or shuffle - duh!) it has pretty much the same height and width measurements. It's even the same (on paper) as the even older pre-video iPods (2G Touchwheel, 3G Clickwheel, and 4G color). And it's only 2.5mm longer than the original 5GB/10GB/20GB touchwheel iPod.
So it may well fit your existing case, with a little squeezing here and there.
But if a case is taking all that the battering and scratching away from the iPod, it's likely to be looking a bit beaten up itself by now. So is it time to treat yourself to a new one?
There aren't too many cases specifically for the new 120GB iPod classic, but remember that any for the 80GB/160GB iPod classic should work just as well. (Indeed it's exactly the same height/width/depth as the previous 80GB classic.)
Belkin has several iPod classic cases.
The Belkin Leather Sleeve for iPod classic is slim and smart in either black, chocolate brown or pink - each with stitching.
Of course it offers access to all the ports and hold switch, as well as the clickwheel, while protecting the case. The screen is further protected from scratches and rain by a thin layer of clear plastic. Unlike Belkin's Leather Folio case there is no full cover, so the clickwheel can be exposed to the outside world.
A Velcro fastening keeps the iPod from slipping out.