These sites are all free for employers (they take a cut of freelancers' pay) and will automatically send out the proper 1099 tax forms
Best for keeping tabs: oDesk The service requires its contractors to use software that delivers screen shots of their work to clients six times per hour. It also supports webcams, so you literally see if your programmer is working. oDesk also incorporates popular software development tools.
Best for repeat customers: Guru When you pay for a project by check or wire transfer, Guru gives you 1 percent to 2 percent back in "loyalty dollars" to spend on future projects. On this site, you can easily browse through sample projects from freelancers. Also, instead of letting anyone bid on a project, companies can restrict bidding to a select group of contractors.
Best for communicating: Elance Elance provides a shared workspace in which clients can monitor project progress. Plus, companies that don't want to be contacted directly by their contractors can do phone interviews without revealing the number. Click a button, and Elance rings both parties. And Elance makes it easy to set milestones and dole out payments as work is completed.
Best for guaranteed results: RentACoder This site lets companies require an "expert guarantee." That means that the contractor must put his own money -- typically a percentage of the contract amount -- into escrow. If the project isn't completed as promised, the contractor loses his deposit. Employers can also require bidders to sign a nondisclosure agreement.