For writing I really like iWriter.com. You pick your rates and can turn down anything you don't like. For designing definitely go with 99designs.com.
One more vote for SEOClerks . As a seller you got many feature that you can use to promote your service and if you don't want to use them your service will also get a nice exposure. The support is great and they always have a fair attitude on any problem. They have many category so you can get targeted traffic. And I also have a great experience with them, no payment limits and no fees.