No one mentioned Denham, where United Biscuits used to keep their King Air
(was flown circa 22 years ago by someone called Dave Ward). The chopper was based there for the Bond film flying around London and the flying wheelchair stunt. Saw the chair set up, it was slung under the Jet Ranger, then the editors/special effects guys got to work to make it all look real. Pilot was an American, who was sadly killed a little while later on a stunt back in the States.
It was also here that the Blenheim, after its first rebuild, did a touch and didn't go, ending up in the trees at an air show. Used to keep helicopters that I repossessed there.
Also used to keep some repossessed light planes and plant at Elstree and knew Spencer Flack, who looked after them for my then employer.
Bovingdon is now partly built on as HM Prison, The Mount and there is a large Saturday market on part of the remaining runways.
Leavsden is now a film studio, where one of the Bond films was shot and I think the Harry Potter films.