http://unixwiz.net/techtips/be-consultant.html
It's about consulting, but it applies to freelancing as well. Good discussion of rates and what people really want in terms of service and deliverables when they hire you. Very good article, there's been discussion here on HN about it too if you go to searchyc.com.
Other things to think about: Elance, Odesk, Rentacoder, or other sites that let you make some cash would be smart to look into, and look at OSS for an option to do some interesting work with smart people.