There are several good sites where you can either load up a job that you want doing and freelancers bid or apply for that job, or you can simply look through and check out their portfolios.
These are O'desk.com and peopleperhour.com. Past users give the freelancers a review rating on how well they completed the role, so you can choose based on reputation. I personally have not found these to have great quality candidates on there, although you do get what you pay for. I tend to go by word of mouth, if a friend recommends a company/freelancer then I am so much keener to use them.
My preferred method in your case might be to find some Wordpress sites you particularly like, and look to see who these have been made by.
Here are some other sites that are highly rated by others in the field although I don't have first hand experience with them:
You can post jobs on all of these with no obligation of hiring someone if you cannot find a suitable candidate.