The variety of work is diverse from web programming, administrative support, sales and marketing, legal work and engineering. The flexibility and variety of work means that many people can find something. As long as you do the project that you are assigned, you are free to go anywhere and live anywhere you want. It is like having a full time job with the ability to travel as you do it.
Elance is the most popular site for people looking for freelance work while traveling, but there are many other freelance websites.
Before we get to the list though I would like to mention that as FreelanceSwitch is fast becoming the destination of choice for freelancers we will be adding our own job board for listing freelance gigs. It's arriving in a fortnight and for the first three months job listings will be totally free of charge to help get the board running.