MyLikes. This works by giving you short ads that you can tweet - this is done directly from the MyLikes website rather from Twitter itself. You then receive a small payment every time the ad is clicked on. To boost the chances of receiving clicks you can also connect your profiles from various other social networks including Blogger, Posterous, Facebook, YouTube, FriendFeed and Tumblr. By connecting these your ad will automatically post to each of these networks (although you can decide which ones you wish to post to).
However, you should be aware that you are not paid for ads that are clicked on via Facebook. So, why connect your Facebook profile? Well, some advertisers insist that you do for opportunities to be open to you.
There will be some people who will be uneasy about having advertising links in their Twitter stream and on social networks. However, the ads are clearly marked as such so you are being completely transparent. You should not expect to make loads of money from it, but for a few minutes at a time I think it is worth giving a try.
Join MyLikes here