Here's one that I've used several times in the past.  Microsoft has a virtual CD Control Panel that let's you mount an ISO image as a drive letter.  This is really handy if you have an MSDN subscription and are constantly downloading ISO's from the MSDN site.  Instead of burning each ISO to a CD you can keep it on a local or network drive and simply mount it as needed.  This will save the cost of a CD and the clutter of having a bunch of CD's laying around.

I've tested this only under Windows XP.

Here's the link:
Virtual CD-ROM Control Panel

This one is destined for the Pragmatic SDK.