My interests include programming, photography and music (guitar), but I've only been able to make money as a professional programmer.
My most successful side project:
Something I wrote as a CS student. It was an online ordering system for a Chinese restaurant. It used an open source fax api component, was php based and put together over a few weekends. It generated over 300K in revenues over a period of 3 years, and was then replaced by GrubHub.