NewerTech 1.8m (72") Mini DisplayPort Cable, Male to Male, White by OWC

Works with any Mac or PC with a Mini DisplayPort
This NewerTech cable will allow you to pass through audio and video from your Mini DisplayPort equipped Mac to a 27″ Apple® iMac via Apple's 'Target Display Mode' to make use of its large screen and audio system. Additionally, you can use this high quality cable to connect a Mini DisplayPort equipped Mac or PC to a display/monitor with an available Mini DisplayPort input connection.

Works with (Mini DisplayPort):
MacBook®, MacBook Pro, MacBook Air®, iMac®, Mac® mini and Mac Pro

OWC Note: As Thunderbolt is based on DisplayPort technology, any Mini DisplayPort cable or adapter is compatible with your Thunderbolt port, too. However 'Target Display Mode' on Thunderbolt equipped Macs require a Thunderbolt cable.