I'd call it proprietary at this point. Aside of Apple's 24" LCD, there are none on the market. Effing ridiculous that if I want to attach a monitor to my MB that I have to buy an overpriced Apple display or overpriced Apple display adapter that should have been included in the box.
Apple's 24" ACD is NOT overpriced. You get speakers, iSight, power adapter, AND it's LED backlit. LED backlit is the key term(s) here. Normal displays like my own are CCFL backlit and fade/dim after a few years. LED is brighter and much cleaner (environmentally). It uses less power too.