For all those using primarily the Google Calendar, there is a very nice calendar that you can import into yours so that you can search and browse all GT sports events (like Le Mans, ALMS, LMS, AsLMS, FIA GT, ...):
Check out the instructions here:
http://baszero.ch/racing/race-calendar/All events that are maintained in the calendar are listed here:
http://baszero.ch/racing/race-calendar/events/I hope this is useful for anybody else too :-)