I just used Protoshare (http://www.protoshare.com http://www.protoshare.com) on a recent project, and it's a very good web-based tool for making clickable proto

I just used Protoshare (http://www.protoshare.com http://www.protoshare.com) on a recent project, and it's a very good web-based tool for making clickable prototypes. It has good discussion features and there's an entire workflow for doing both wireframes and design comps as you get further along in the project.