Balsamiq is a great mockup tool - it's quick and simple to use. The Balsamiq champions blog is a series of articles by people who have put it to good use. Worth a look if you prototype (or are wondering why you should) - even if you use a tool other than Balsamiq.
We're lucky at the University of Edinburgh to have the prototyping tool Balsamiq freely available to all staff and students via our wiki service. My team make good use of it, and I know others do too.
We set up a dedcicated wiki space for prototyping specifically to encourage colleagues to do their work in the same place which encourages us to have a nosey at others' efforts. Sometimes seeing what others have done is a great way to inspire us.
And of course, on this blog, the examples are in a totally different league to anything we do. Some nice screenshots and videos to illustrate stories of collaboration, design exploration and user testing.
Balsamiq champions blog