-kray
I use
this for my 12PB.
Seems to hit every mark you are looking for. I use this one for video editing, but there is a 'little brother' that is 4500RPM and smaller cache if you don't require the bandwidth (save $100).
These are FireWire bus powered - truly portable and small (about the size of a Pocket PC). It does come with an external cord if you wish to plug it in, but I've never used it. No drivers, just unpack, flip the little switch to "bus power", plug it in, and it'll mount. Still have to drag to trash before unplugging, otherwise you'll get the "data might be lost" message.