Hi, a friend of mine had an Advent Laptop with a 40GB hard drive which he has almost filled. He's looking to buy an external drive around 120 - 160GB. He has both USB 2 and Firewire.
The drive will mainly be used as extra storage, but he does a lot of travelling and often wants to put his music & video on there so need somthing that will stream data nicely. At the moment from reading reviews and because it has the higher transfer rate Firewire is favorite. Quieter is also better.
Maxtor are absolutely superb, a little bit cheaper too. I don't think you can go far wrong with either.
On the maxtor I found usb2 and firewire to be about the same. USB2 slightly faster, bit more of a resource hogger. With the maxtor you get everything you need in the box. Cables (USB2 and firewire), backup software etc. R
Both models need external power to operate. So they are not suitable for your friends. What your friends need is external HDD (2.5" version) which can be powered by usb port of laptop. Here are a few examples: click hereclick hereclick here. They are expensive than 3.5" version, but they are truely portable, just plug into usb port of laptop no need for extra power unit. They are firewire version as well.
An cheaper is to get a 2.5" laptop HDD (e.g. 80GB for £150 click here) and then get an external enclosure for it:£16.99 click here).