Christian, try these:
These are some of my favorite places to keep track of the designs and designers. These are places where the best designers like to show ase work. Spend some time on them, find sites you like and see who designed them. There are good freelancers and boutique studios out there.
Some thoughts on working with designers:
-- Vet the portfolio, what you see is what you'll get since individual designers have particular styles.
-- Front-end programming skills are not the same thing as visual design skills. Two different disciplines. Again make sure you vet the portfolio to make sure you are comfortable with the visual style.
-- Design is service and as such is a function of time. The best designers tend to cost more because they spend more time thinking about your project and fine-tuning it. They don't treat their work as a commodity.
-- The best clients are neither too hands on nor too hands off. You want to give your designer a comprehensive brief at the beginning and constructive feedback throughout the process. But don't micromanage her or you may miss out on her surprising you.
I wouldn't go with elance.com or similar bc the quality of the design offered is mixed. I also don't like contest sites because you are asking a lot of people to work for free, and that's not good for the design profession. Choose a designer like you would a doctor and develop a long term working relationship.
Let me know if you need any more help.