Twaitter

Twaitter is a pretty robust tool that allows you to schedule your tweets for later, among many other things. The interface is very simple to use. You can schedule tweets out whenever you like and can create recurring ones as well.

It can serve as your Twitter client as well - meaning you can send a tweet from here as well in additional to seeing who you are following (you can unfollow if you like) and who is following you. To use, just login using your Twitter user name and password and away you go!