I told you about the showcase forum at Joomla a few weeks ago but now there is a dedicated home for showing off your Joomla sites. The Joomla Showcase is a great place to check out what others are doing with Joomla. There are already over 200 listings and if you think your site is worthy, you should request it to be included.
Update 19 NOV 2010: There are now over 2000 listings.