Epinions, a very popular product review site, established by paying people to write the reviews. There site has prove very popular so don’t feel ashamed if you want to go down the incentives submission route. Sometimes, it can be the perfect way to offer the necessary impetus to get this kind of content generation under way.
This is merely the tip of the iceberg as far as user generated content is concerned. Whether it’s a review of a product just like xsitepro review, a post on a message board, or comment about a blog post or article - it’s all additional content that you can profit directly from and yet it’s all being generated for you, with very little exertion on your part.