I have used PayPerPost on this site a couple of times, (you can see the posts under the Paid Advertising category. PayPerPost is a blog advertising tool that allows you to get paid to investigate and write about a particular company, blog or topic.
PayPerPost recently decided to make it mandatory that all PayPerPost bloggers reveal that the posts are paid ads. I think this is a good idea.
My experience with PayPerPost has helped me with my writing skills and earned me a few bucks. If you would like to make some extra money with your blog or if you would like to place some ads on blogs check out PayPerPost.