You’ve gotten some good suggestions, just a couple of other thoughts to keep in mind:
Tests at barefeats.com show some interesting comparisons between 5400 and 7200 rpm drives. Walter is right to point out how much drives slow down when they fill up, however that very reason is pointed out in the barefeats test to show that larger capacity 5400 rpm drives can often be faster in real world situations when you are sticking to portable designs. It comes down to how much you want to spend.
If you can only afford single drives and you want the 2.5″ form factor, I think you’re limited to 100GB if you want a 7200rpm drive. You can get a 160GB 5400rpm drive for less money. If you have say, 70 or 80GB of data already on the drive, the 5400 drive is actually faster at that point, since it’s a little over half full while the 100GB drive is at 70 or 80 percent capacity.
I went with a 160GB, 5400rpm Hitachi drive in a transinternational Minixpress box:
https://www.transintl.com/store/category.cfm?category=2643
It’s got USB 2, Firewire 400 and Firewire 800 interfaces. You can buy the case bare, or they sell a selection of drives installed. It was actually cheaper to buy the drive from them. It’s also bus powered which I love. No power brick to carry around, and no need for an a/c source to be able to use it.
The G-Raid mini is also a great choice if you have the money. Lacie also makes a bus powered, two drive array. These are great as you can have both large capacity and 7200rpm drives. They are, naturaly, a bit bigger and heavier.
Firewire 800 makes a BIG difference in read/write speeds, but only the latest Macbook Pro machines have a FW800 port. You can get an expresscard adaptor, but you may not be able to use a bus powered drive through it. I bought a cardbus card for my Powerbook G4 and it does NOT power the drive.
Regards,
David