Whilst working at Latitude a couple of my clients used Adfero to supply keyword rich articles. They basically supplied a RSS feed which we then implemented into the website as a news section. The aritcles are unique and relevant to whatever subjects you agree with Adfero, I think you have to pay a bit extra if you want images or articles over 500 words.
All in all, a very good service. For an example of a website using their articles see
MoneySolve