•Kaboom!
This finder is mostly for playspaces such as playgrounds, pools, and skate parks, but it also includes some nature trails. Click on "search by playspace name" and enter "trail" in the search box (this isn't perfect but it's a start). You can also submit your own favorites.More »•EveryTrail Mobile App
EveryTrail is a resource for geo-tagged, user-generatedtravel content from over 80 countries. Search for an interactive map and see others' photos of the route; you can use EveryTrail for road trips, hiking, geocaching, biking, snowshoeing, and more. Apps are available for iPhone, Android, BlackBerry, and Windows Mobile.More »