I don't know where you are but pactec.com and serpac.com have lots of different cases and they are carried by many distributors. I don't recall a cut out for for usb but they have several that are pretty easy to modify with a nibbler.
a dremel is a great tool but hard to control and square holes are very hard to do.... I have one and a nibbler.
The nibbler works on plastic and metal. It cuts square chunks out so with a little care, you can cut square holes (first drill out a hole). It's pretty cheap. I think they are both very useful..
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I agree that both tools are great and personally use both. I just find that with sme practice I can do quite intricate cutouts rather than just square/round