External -> firewire if you need speed. I just bought Lacie/Porsche 250GB and it was preformatted so no hassles there. I chose USB 2.0 model because of compatibility (laptop etc) knowing it would be slower. But it really was a plug-n-play operation to get it running and the drive itself cost under 100€. And it looks posh too! :)
http://www.lacie.com/fi/products/product.htm?pid=10468
http://www.lacie.com/fi/products/product.htm?pid=10468