Elance - The largest online freelance site. Probably the best site if you want a large professional job. However if you are looking at a smaller job or you want to cut costs to the bone you may be better off with Rentacoder or Scriptlance. Elance charges the freelance providers to just be listed on the site, whereas Rentacoder and Scriptlance only charge the providers once a project has been selected.
Rentacoder - Probably the second largest coding freelance site. Worth checking out. When you get a project done through Rentacoder you put the entire project fees into an escrow account. You don't release the fees until the project is complete. This is good because it gives reassurance to the coder that they are going to pay you, but it also can be difficult if you have a large project, because you have to pay the entire amount into an escrow account, although you can put the project into stages and pay based on each stage.
Scriptlance - This site has the lowest costs but it doesn't have some of the features of Elance and Rentacoder. Not as professional but good if you want really cheap coding.
Getafreelancer.com - Another reasonably good freelancing site
Guru - quite a large outsourcing site
Contracted Work - a reasonably sized contracting site
Use Site Build It to build your web site
Site Build - It may be a better option for you than hiring an outside contractor. This software will give you high ranking on the search engines as well as have your own email list and hosting all included. It is a much easier option and has several tools included that help you to build your own site without any knowledge of HTML. The best thing about this tool is that it helps you to get high rankings in the search engines and has lots of bonuses included. You can also hire someone to use the Site Build It software and do everything for you if you want.
Some smaller outsourcing sites:
Oslance - open source projects
Projects Pool - a smaller outsourcing site
Dev Bistro - online job postings for developers
IT jobs - job listing site
PHP Career - list of resumes of developers