BuySellAds is a popular online ad network where web publishers can easily find sponsores for websites, email newsletters and even Twitter.
Publishers can go for CPC based ads (per click) or CPM based ads (per 1000 impressions) and BuySellAds will take a 30% commission. They have a huge pool of advertisers who can also look at a blog’s influence /reach before buying an ad.
Celebritries like Paris Hilton use BuySellAds to sell sponsored tweets to their millions of followers on Twitter. You can also use BuySellAds to monetize your email newsletters and RSS feeds.