People just getting into information architecture (t d) frequently ask me which application to use for creating wireframes. After nearly a decade of making wireframes myself, I still ask this question on a client-by-client basis if not a project-by-project basis.
Garrick needs to add Dia to his list of applications/technologies useful in creating wireframes. Dia is an open source (meaning, among other things, it’s free) Visio. It’s young, but promising. Here is Dia’s project page