Here's a fascinating article from The Future of Music detailing the forty-two ways musicians can make money these days. They start with the most obvious and then work into things that are a little more, well, esoteric.
Because everything musician's situation is different, some will be more doable/practical than others. Some methods will be totally out of the question.
Still it's a great read, especially if you're trying to make a living wage as a professional musician.