This door, made with RedPower 2, vanilla pistons and Computer Craft uses CC's floppies as access cards.
Features:
  • Each card gets a unqiue ID, allowing you to shutout unwanted personal.
  • System is expandable to as many doors as you can fit.
  • System can be used for many other redstone applications, such as card controlled machines.
  • Cards (appear to) load from disk on boot. No promises thou.
The door is quite simple, it uses a mode system to work out what to do on various events. For example exiting the door from the server room sets it in mode 1. In mode 1 it ignores redstone from the inner pressure plates, ignores disks and shuts the door on redstone from the exterior plates. Putting a valid disk in it (it will check the disk is formatted properly, then check with the server to see if it is a real card) puts it in mode 2, which does the the opposite.

I'll post the code once I've cleaned everything up.

Sorry about the video's quality. It looked great on my PC after compression, but Youtube has degraded it.
http://www.youtube.com/watch?v=BznqLsCC7XA