FakeTweet

Rebecca Small is a fellow social studies teacher and a teacher-student in my class learning to integrate technology into the classroom.  She just made this very nice assignment for her students using FakeTweet.  You could copy it and completely change the assignment to match your needs as it has a link to a great how-to video (made by a former student of mine) as well as an example of her FakeTweet and, of course, a link to the FakeTweet maker.