Kumomo

Kumomo is a relatively new website where website publishers can sell any type of ad space. It's sort of classified ads on newspaper. There is no banner format like Leaderboard or Wide Skyscraper. Basically, you will just have to decide what to sell and then set a monthly fee.

Kumomo's ad manager for publishers is very simple and easy to use in a sense. First, you need to register an account. In this process, you will create a profile, describing your website, providing the URL, monthly number of unique visitors, site language and so forth. The next step is to create an Ad. Again, there is no ad format. So you decide on the size by providing horizontal and vertical number of pixels. You will then get to decide on the monthly rent for your space.

Unlike other advertising networks, publishers are required to spend at least 1% of ad revenue to a charity. Acording to its website, they are raising money to build school in Cambodia.

By the way, Kumomo has no power in enforcing a contract between a buyer and a seller. So when the publisher refuses to fulfill a contract in placing ads after receiving money through PayPal, the best that the space buyer could do is to write a negative review at seller's page.