I'd also like to recommend mftpg - although you'll have to wait in line
Saw NPG's thread and decided to give him a try. I received the first 2 articles from him yesterday, and was very impressed with the quality. Spot on for accuracy and intelligently written - much better than I expected and written with integration into the site in mind, perfect. They also arrived when he said they would, and a great price too.
I'm just drawing up a list to keep him busy for quite a while. If you've had trouble finding decent writers, give him a try - I don't think you'll be disappointed.