This is a Creative Commons Google slideshow that shares 34 interesting ways Twitter can be used in an educational setting. It is definitely worth a read - knowing if you pull one new thing out of here to use, you have already put a step closer to engaging your students in a new or different way! Why not try?
This site allows you to search any word and see different meanings and associations with other words. This could be helpful for students when learning new vocabulary or even old vocabulary and discussing which meanings are applicable to your subject and what you are learning in the classroom.