I have worked with LifeTips on behalf of two clients now, and highly recommend their services if the section you want is not already taken. I do have my doubts about how much link popularity the links from their site pass on, but that is really beside the point. Campaign tracking has proved to me that, at worst, you will gain your money back from sales or referrals that come directly from the section you sponsor on LifeTips, and the free text link and banner ads (on other sections) that come with a sponsorship account. 

Here is an example of a LifeTips section. It is sponsored by Gaiam Yoga. LifeTips has written dozens of pages in this section, each one of them providing a useful yoga tip and linking to the Gaiam website. Notice the ads running down the right side. They look like Google Adsense ads, but they are actually free ads posted by other sponsors. Also, notice the small button-like advertisements at the bottom of the page. Those too are free ads posted by other sponsors in similar markets.

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