You may have heard of an alternative to AdSense called in-text advertising
In-Text advertising inserts text link advertisements within the content of your blog. If you look at this website, you’ll see the double-underline hyperlinks. Upon a hover of the mouse, a floating informational bubble opens with content from an advertiser. If clicked, the visitor is directed to the advertiser’s landing page and you earn advertising revenue.
Because in-text advertising shows up in the main text of your blog, it has much higher click-through rate, comparing with AdSense. There are a few in-text advertising providers, to name a few, AdBrit, InfoLinks and Kontera. Among the three, InfoLinks seem to pay the highest.