Internet Movie Plane Data Base
Lots of aircraft that have appeared in films and on TV.
Helicopters (some overlap with the above, gives more details about movies, TV show episodes, etc.)
Internet Movie Firearm Data Base
As above but guns, seems to have more TV shows.
Internet Movie Car Data Base
You have to search for specific movies / shows or for a specific type of car rather than browsing, and there isn't as much information about specific episodes or movies as there is in the other databases, but it seems fairly comprehensive. Also covers buses, motorbikes, trucks etc.