I have found the best way to find a good designer is to look at the sites you really like visually. These days most web developers / design companies work globally. So, if you see a site you like, take a look at the credits in the footer at the bottom of the page - that's where most sites put them. Then take a look at the designer's own website and their portfolio.
After that, it's a matter of making some calls and interviewing them. If you hit it off, you can ask for a concept and quote.
Hope this helps... good luck.