As a freelance writer myself, I'm always looking for books to give me ideas or help me hone by craft. I don't put much stock in the idea that I can become a better writer (or a "real" writer) by reading lots of books about it - in my opinion, that just takes more time away from writing - but there are definitely books out there that contain valuable information. The one I'm reading right now, Make a Real Living as a Freelance Writer by Jenna Glatzer, seems to have a lot more (and better!) information than most.
What I like about Glatzer's book is that it contains a lot of "insider's secrets" - tips and tricks that you usually don't learn until you're well entrenched in the business already. However, many of these tips - like what types of stories to pitch to editors when you're first starting out, and how to pitch - would be extremely helpful for beginning writers.
When I'm finished reading the book, I'll give it a more detailed review on my Reading 4 Writers blog.