Tim Sneath has been doing a great job of blogging the many Vista/WPF showcase applications that are being deployed right now. If you are looking for a quick list of URLs that you can hit for the .XBAP or .APPLICATION files, please go to the WPF Application Portfolio wiki, which I've updated with all the links, tagging them with the kind of deployment used -- very cool to see the number of .application and .xbap applications out there! If you are doing a demo and trying to show someone the WPF portfolio, hopefully this wiki page will be useful -- and watch for more coming...
I've also added some that Tim hasn't documented yet, in particular a whole bunch from Japan, as well as one from Metaliq on snowboarding visualization. Some screenshots below.