Twitter is sometimes considered a tool that is "a solution looking for a problem to solve." it is cool and immediate and useful for people to keep in touch. Here are some resources that educators will hopefully find useful when considering using Twitter in their classrooms.
Twitter Handbook for Teachers
An 18-page ebook for teachers. Begins with a basic intro about Twitter and then provides insight about using Twitter in the classroom. These ideas are from teachers and written for teachers.
Twitter for Teachers
A collaboratively-written, wiki-based ebook to "Teach Teachers about Twitter."
Twitter 4 Teachers
Another wiki created to help teachers find teachers through Twitter. This can be quite valuable if you want to find a group of twitterers in your field of instruction.
"Where Do You Learn?": Tweeting to Inform Learning Space Development
An EduCause article about how you can use twitter to provide real-time information about your learning environment.
Twitter Tips: For Teachers and Educators
David Hopkins' Overview of how and why to use Twitter in education.
Twitter in the Classroom (YouTube Video)
In this 9-minute video a high school AP Biology teacher tells how he uses Twitter in his classroom. Begins with an explanation of Twitter and then discusses the applications.