I came across this article at Wired that talks about how a new concept mapping tool that they hope will preserve scientific knowledge, and will serve to help students learn.
My favorite quote from the Wired article; "We need to move education from a memorizing system and repetitive system to a dynamic system,"
Amen to that.
My favorite quote from the mapping site: "The CmapTools client is free for use by anybody, whether its use is commercial or non-commercial. In particular, schools and universities are encouraged to download it and install it in as many computers as desired, and students and teachers may make copies of it and install it at home."
Another free concept mapping tool is Freemind. It can be found here.