DVD: ITV-ATV (Associated Television) The Elstree Story
Not sure how useful it'd be, it's hard to tell if it will have any footage of Elstree studios, or just clips of programs made there.
If it's stills you're after, I assume you're already familiar these Elstree websites.
http://www.elstreefilmstudios.co.uk/
http://www.elstree.co.uk/index.php?page=history
Elstree Calling
That last one has a good page on the George Lucas Stage with a couple of construction photos.
And this page has some good exterior shots of the site in its heyday before Tescos got built on it.
As for footage - off hand I know 'Return of the Ewok' has some shots of the studio (presumably Elstree) - both exteriors and interiors (e.g. star dressing rooms).
And the 'Risk Business' program on Babyhum's BH018 Making of the Myth DVD has lots of interior set shots from Empire. It also has some nice exterior shots but they're of Bray Studios. Shame.
'The Making of Temple of Doom' has some interior set shots, and guessing 'Great Movie Stunts: Raiders of the Lost Ark' also has some set shots. Those two and the 'Making of Raiders' were preserved by DigitalfreakNYC and upped to the spleen a while back (as were the above star wars docs), along with similar preservations by THE ARCHIVIST. The Raiders docs were Laserdisc > DVD transfers, and either of these preservations will probably be the best quality you're going to get, this side of an official release.