with freelance writing? Then Elance would be my suggested source. I have been working as a freelance writer for 4 years and have found most of my current employers throught this site. They do require that you sign up for a subscription and there is a monthly payment of around $12 per month, but when you are actively working through Elance that is a very small fee. They usually have around 750 jobs posted, so there is ample opportunity to find a job that fits your expertise.
Elance works on a bidding system somewhat similar to ebay, except you are bidding on a job. My biggest suggestion for being successful in winning jobs is that you should customize every single submission you make for a job. Some people have one submission blurb that they use for every job they are bidding on, and it is very obvious to a buyer when someone is doing this. Also, always submit a couple of samples of your work, whether it is asked for or not.