They have created two tools, Finder! and Maker!. If you go directly to their "finder," you get a simple search field that delivers search results and other possible tags that might relate. For the items I found today, there was a *.kml, a *.csv and a *.shp for each one. I'm not saying this is the only source, but the folks over at GeoCommons have made it nice and clean for us to get data!
Grab your butterfly net and visit them at http://www.geocommons.com for some data!