There are two books I'm excited about right now. One of which I'm reading and one that I am about to read:
Beyond Talent: Creating a Successful Career in Music  by Angela Myles Beeching and
The Savvy Musician: Building a Career, Earning a Living & Making a Difference by David Cutler

Both are based on the principle that Musicians need to be entrepreneurs and think outside the box to make a way for themselves in this difficult profession. The first seems to be more along the lines of promoting yourself as a musician and bringing what you have to offer to the table. The second seems to be more about engaging your entrepreneurial spirit. It has many many examples of people who created a place for themselves in an unusual way. We have to be honest about what it means to be a successful musician. Not every flute player can be Principal Flute of the New York Philharmonic, only one. But that doesn't mean that our talents aren't useful in other places.
I highly recommend either of these books for Music Majors in college ore anyone who is looking into a career in music. We spend so much time as a student practicing, and trying to be the best musicians we can be, that when we get out... we don't quite know what to do next. These books won't answer that HUGE question, but they might give you some tools to help guide you in a new direction, or inspire you to continue to find your own way.
I wish I had come across a book like these several years ago, I think my life would be in a different place by now. Then again, I may not have been ready to understand... After all, Liz (my flute instructor in college, for those who don't know) was trying to teach me all these principles all along!