Twitter is hot and has become a service to advertise on either by the proprietary advertising system or by Twitter applications relying on the service to send advertising messages. A recommendable service to do so and to earn money with by sending out promotional tweets is SponsoredTweets.
I do participate in the service myself and just logged in to review some opportunities I have been informed about by email. At first it is noteworthy that the service has advertisers available paying for sending out messages and secondly the possible income is reasonable. The minimum amount one may earn for a click on a tweet sent out is 10 cents. But it comes even better. I am using the service in combination with another account, which has about 190 followers @emediablogger. This amount of followers is not much, but the service recommends me to set my price up to 71 cents. So earning about 70 cents by one click and with an account having a fair amount of followers really is a good deal and gave me reason to post this review about the service. Last but not least the service is running a referral program with further business opportunities by referring others and advertisers. To join visit SponsoredTweets.