A site that I not only built initially, but also managed for many months is the Wrox P2P forums site. This site was intended to let readers of Wrox Press books communicate on specific book related subject areas and solve their own problems.

The story of it is worth relating, my then boss liked new gadgets and wanted instant results and bought the Lyris server. I installed it, got it up and running to find a completely vile and un-user friendly front end. However Lyris exposes its APIs and so it was a doddle to get ASP and remodel the whole front end. It now serves thousands of readers and has an active membership of way over 20,000. I'm still an active contributor on it and blogged for a while there as well.