The dealer locator is built using the Drupal GMAP and Location modules in conjunction with my own bespoke module.
The bespoke module makes it possible to pull location data from a central source in a multi-site Drupal environment. Armour Automotive owns a number of audio and automotive brands and the ability to easily manage all their dealer location information in one central location and have it automatically published to the appropriate "brand" site has been both an eye opener and a time saver for Armour.
The past few months has seen heavy investment by Armour in re-vamping 10 brand websites using Drupal 7 and yours truly helping with the technical stuff. It's been a very busy few months to say the least, but I'll be publishing details of some great new Drupal 7 sites in hopefully the next few days.
Much of the credit for the ArmourAuto.com site has to go to James Hoskins and Stuart Ephgrave (both at Armour) who have put a lot of high quality work into making great content for the Armour site - not to mention, believing in the possibilities ...
Edit: A link to a more recent (and more advanced) map I've built www.shopgreenwich.co.uk/map. Source code for the Drupal module is provided in the comments for anyone interested.