When I switch to freelancing, I started with Toptal while trying to build my network. They run you through a standard startup-type interview process, then once you're in, they take care of the finding clients and managing payment part. They sell the client on a rate, you set your rate, and they take the (unknown) difference. The clients went from being put on an existing team to building a team and launching a startup product. Overall it was a mostly positive experience. You can email me (in my profile) if you have questions.

Then, while doing that, I worked my network and found a couple good clients. I also posted in the monthly Freelance thread here on HN. I found two great clients through that!