Websites for Composers and Musicians
How about a design and hosting business that specializes in sites for musicians? A service to take recordings and convert them to MP3, to offer PDF samples of sheet music, and build a website around them? I think people would pay for that -- probably an upfront design fee and then a minimal monthly hosting fee.
Steganography
Okay, and this one is less a "business" idea and more just a fun thing I'd like to do: e-Steg.
A standalone, easy-to-use interface to create eBay auctions whose sole purpose is to carry covert messages. With the eBay API and a collection of Java steg classes already available, it just needs someone with the skill and drive to create a front-end and make it work.
I happen to know just such a person... Hee hee...