"Thunderbolt combines PCI Express and DisplayPort into one high-speed, versatile I/O technology."
-- Apple, Mac Pro webpage
That means you can still use DisplayPort monitors too, just like you do with existing Apples that have Thunderbolt ports. There's no need for adapters either, just a mini-DP to mini-DP or DP cable. In fact you can even use mini-DP to DVI cables (I'm literally doing it right now).