Should I get a mini DisplayPort to DVI or HDMI to DVI adapter?
Additionally, don't forget that Thunderbolt really means mini DisplayPort where video adapters are being considered. Since a DVI connection is required for your external display get something that will end in a DVI connection. Additionally don't forget to shop around for adapters, places like MonoPrice can help you save a bundle on adapters and Cables when compared to retail prices.

Solutions:


Mini DisplayPort to DVI adapter (from MonoPrice)
HDMI to DVI adapter (from MonoPrice)