Ok, I will say first that I'm not a (successfull) freelancer (yet), I'm trying to be one of, but still in search of which niche that I could and should enter. Here I will give short explaination about several freelancer site which some freelancer said it's a good site to search, bid, and get a job. This list is in no particular order.
RentACoder.com (Start, January 2001)
Quote From RentACoder About Page
Rent a coder was the brainchild of Ian Ippolito, the CEO of Exhedra Solutions, Inc. As a programmer himself, Ian had been receiving too many requests for custom programming. After turning away paying customer after paying customer he realized that there was a need that was not being met. In January of 2001 he began sketching out the idea while on training trips and a long vacation in Italy. By the middle of the year the site was ready to go live. A year later in March 2003, the site facilitated 1,478 successful software projects per month, and that number has grown substantially since (up to date stats are here). The majority of buyers on the site are from the United States, the United Kingdom and Australia (in order of volume). The majority of coders are from the United States, India and Romania (in order of volume).
Guru.com (USA, started August 2000)
Guru.com originated in 1998 as SOFTmoonlighter.com and several other similar sites that consolidated as A2Zmoonlighter.com in 2000.
In Less than one year, the site attracted more than 50,000 registered users. Guru's Mission is to provide businesses with the most efficient platform to connect and perform transactions with freelance professionals locally, nationally, and globally.
elance.com (USA, Founded in 1998)
One of the largest freelance sites. Elance charges the freelance providers to just be listed on the sites so if you have no money to spend, you might want to choose Scriptlance or RentACoder.
Scriptlance.com (Canada, started in 2001)
Scriptlance provides users with escrow payment options to help projects get completed smoothly. Best if you want really cheap coding
GetAFreelancer.com (Sweden, started in February 2004)
For Professional programmers, interpreters and graphic designers. There is a free escrow system for freelancers and buyers