A couple of good freeware programes: LiteIcon and AppCleaner.
I had an odd issue of the icon for my NAS reverting every time I tried to change it. LiteIcon solved that issue for me; it allows for the changing of the default icon for any number of things. You can get it here.
My second application stemmed from the first. You will remember AppTrap from a few posts back. This one does more or less the same thing, but with a bit more in the feature department. AppCleaner is an application (rather than just a preference pane) that does the same things as AppTrap, but also allows you to remove widgits, preference panes, and other such files. A good thing to have around. It also can be found here at FreeMacSoft.