I've run this as my TM backup device since Leopard came out and it's flawless. Connects via FW400/800 or good old USB. Auto-power option but I usually just flick the switch, let it mount and run a backup every day or so, then dismount and power it off.

I've got a Western Digital something or other inside a 2.5" Welland USB/SATA case that works just fine as my MacBook Time Machine, EXCEPT that it negates the whole point of a laptop. It's a pain to have to plug it in, unplug it, plug it in.......

One option would be a Dock with space for a a built-in drive, but I doubt it exists yet and it would add to the weight being lugged around.

The real answer is the Time Capsule. Not cheap, but oh so convenient.

Many choices, but I suggest giving yourself all options - your MBP has USB, FW400 and FW800 - might as well get a drive with the same choices. FWIW, Lacie has worked ok, while Wiebetech and Iomega have been very good as well.

USB2.0 may have higher on-paper specs than FW400, in my use it is slower 99% of the time.

Formatted for Mac, comes with all the FW inputs to get the best from the MBP, fanless so it's very quiet and cheap too!

However, unless you use it in place a lot and having an external hard drive docked is convenient, as said above a Time Capsule really is the best option... factor in the convenience and everything you get and i genuinely don't think they're that pricey - especially if your other half is a student and you get her discount on it :-)

Why not a drive on your LAN? I use a 500GB Iomega on the home network, can access it through wifi => no wires. For big xfers, just connect to the ethernet.