One of the top prototyping tools are now free to students and educators!  DO NOT MISS OUT!!!!

Axure RP gives you the wireframing, prototyping and documentation tools needed to make informed design choices, persuade any skeptics, and document your design… and maybe win a few fans along the way. Choose the Standard edition for prototyping or go Pro to add documentation and collaboration features.

http://www.axure.com/edu