Foursquare
Foursquare is a social-networking Worldwide, location based, community, City-Guide service available for common smartphones, including the iPhone, BlackBerry and Android powered phones. To use Foursquare on these devices, download the free app.
The app's purpose is to help you discover and share information about businesses and attractions around you. You can find there vegetarian friendly, vegetarian and vegan locations (not only restaurants).