It seems like the latest sport out there is looking for Windows SharePoint Server v3 (WSSv3) and Microsoft Office SharePoint Server 2007 (MOSS 2007) sites. There are several blogs posts (which quickly become outdated) trying to list all the public sites that are publicly available. For instance, try these:

Now I was playing around with search and figured that you can find a lot of sites out there using WSS/MOSS by simply searching for certain strings. For instance, you can search for "_layouts" and you most likely will find only SharePoint sites. Try this:

Once you find a site int he list, you can cut/paste just the main URL (before the _layouts) into the browser to go the main site. You can also use the "site" option in the search engine to find just sites in universities or just sites in France, for instance:

You do end up finding a whole lot of sites out there using the technology. As people start customizing WSS/MOSS, it gets harder and harder to figure out the technology behind it. Have fun looking at how people out there deploying SharePoint in public sites, but don't waste too much time browsing the list... :-)