Apple has released a new VESA adapter that allows the new 24" iMac and LED Cinema Display to be mounted to an articulated arm or bracket.

http://store.apple.com/us/product/MB902ZM/A?mco=MzE2OTkyOA

 

This is the first time an iMac has had this feature, and if you ask me, it's about time!  Good move, Apple!!  We've been mounting Cinema Displays to various arms, stands, and other devices for a couple of years here and the flexibility you gain is invaluable.  I can't wait to get my 24" iMac with a 24" external display side by side on arms!