Here is a free service for Twitter users that allows you to automatically send a direct message to anyone who follows you. Called TweetLater, the message can be anything you want and can include a link to your site or an affiliate program that you choose. This is a great way to start interaction with all your followers.
The service comes in 2 kinds, free and paid. The free lets you do what I just mentioned awhile ago. The paid version also provides a different feature letting you schedule to send out tweets to your followers depending on the time that you set.
TweetLater is a tool to boost productivity for Twitter users.