You should look at the Jing project..... it's essentially open source Camtasia 😉
EDIT: Huh... TechSmith creates Camtasia Studio, and they're the ones behind Jing. It's probably the same software just with some limits. So if you can limit your movies to 5 minutes (which is usually a good idea because of internet speeds) stick with the free version 😉 Otherwise, shell out the $300.