Google AdSense

静水流深

https://www.google.com/adsense/
AdSense delivers text-based Google AdWords ads that are relevant to what your readers see on your pages. You get paid when users click on AdWords ads displayed on your site.

You cannot run other text-based ads on the same pages as the Google AdWords ads. This rule applies only to ads that "mimic the look and feel" of AdSense. For example, Amazon.com affiliate links are O.K.

Pop-ups and pop-unders on the same pages as the Google AdWords ads are not allowed too.

Available text-based 468 x 60 banners, 120 x 600 skyscrapers, 728 x 90 leaderboards, and 300 x 250 inline rectangles. You can show only one ad unit per page.

$100.00 minimum payment. Affiliates are paid monthly, within 30 days of the end of month.

Besides English, AdSense publishers now have the option of placing their ad code on pages with content in French, German, Italian, and Spanish.

Currently effetive CPM of AdSense ads on my sites are over $2, with CTR around 1.2 %.

Accepts majority of sites without "excessive advertising".
Recommended.