Best for me would be the G-Tech mini range of portable HDD. They are absolutely superb and come with all of the main interface ports (USB2, FW800 and so on).
Not only that but they come with a nice leather case and all the cables you could ever need in an Apple friendly white.
The make is superb too in aluminum and it looks like a mini MacPro!
Expensive but if you want one of the best they are worth it.
Try
here for the range and some of the best prices.
Mike