If you're looking from something basic, this page uses an AVR microcontroller to read symbols from an ISO card reader. This one uses the same AVR to control a lock on a password match/password fail basis. You could combine the two to build something like what you describe. It can be used to read anything from credit cards to a drivers license or any card with unique content.
Proximity cards are also catching on but I'm unable to find a cheap source on these. Jonathan Westhues has a cool page on building prox card systems from discretes.