This is a fantastic free wireframing and flowchart tool.  I’m a fan of free tools that make things easier, and ones that you can use directly in your browser are even better.  It’s really easy to use and pick up.  Gliffy boasts a wide array of features that every user interface desiger would regularly use: a flow chart designer tool, UI wireframing tools, and even an easy to use sitemap designer tool.  It also comes as a chrome app:  Check It Out