SportingSights has a huge collection of geo-tagged sports stadium. The site seems to have collections for most major sports. Each stadium is shown on Google Maps but there is also the option to view the stadium in Virtual Earth, Yahoo Maps and Multimap.
MapGameday is a website aimed at college football fans to help them share special places around their favourite school with other fans. Users are able to share their favourite hotels, restaurants and tailgate locations.
The site includes a number of Google Maps, such as the college football recruiting map and team travel maps. The team travel maps show the distance that College Football Teams travel for road games, both in and out of conference. Whilst the college recruiting map shows every division one school and their recruits.
MapGameDay also allows you to view the college football stadiums in 3D via the new Google Earth browser plug-in.
Golf Nation has added Google Earth Browser plug-in views to their comprehensive list of golf courses. They have also added the option to embed any of the golf course maps in your own website or blog. Each course has all eighteen holes tagged and each tag contains information about the hole's par and length.
Google Earth Hacks and Google Earth Blog have teamed up to create a web site that allows people to share and view 3D locations using the Google Earth plugin. Combining Google Earth Blog's vast knowledge of Google Earth and the thousands of kml files in existence with Google Earth Hack's experience of creating Google Earth and Google Maps collections is an inspired idea. This site should prove to be very popular
Whilst EarthSwoop is not exclusively devoted to showing 3D sports stadiums some of their early collections do exactly that. Try the tour of NFL Stadiums, or MLB Stadiums.
SatelliteSights.com is a new community-driven satellite image sightseeing project. Users can submit interesting views they have found on Google Maps. The site already has thousands of interesting satellite images from around the world, submitted, researched, and maintained by its users.
Again SatelliteSights is not devoted to just mapping sports stadium but it does include a big 'sports' section of satellite views.
You can find many other Sports related Google Maps Mashups in the right hand column of this page under 'Sports and Events'.