I got an ADS Tech dual link drive kit and stuck a WD 200gig SE in it tonight, I'm pretty happy. The enclosure fits optical drives as well, so it's not small, but it's quiet and seems to work well on usb2 or firewire. The firewire is a good bit faster than the usb2, HDtach shows around 38mpbs burst and a solid 30K on the graph. The drive is a good bit faster than that, I don't know if it's the buss or the enclosure itself limiting it. It does not drag at all though with music or video. It was a little pricy, hundred bucks at circuit city, I know it's probibly available cheaper online, but I have it in my hand NOW, so..
The models with drives already in them are pretty good deals really, I just already had this 200gig, so..