fujitsu makes some good units as well.
the lifebook p1120 is verrry small transmeta 800 w/ 256ram and 30gb hd. starts around $1200
pair it up with a usb based interface, you can record up to 24/48.
for firewire, you would need to add a pcmcia firewire card.
dont know how long the extended battery runs it, but our salespeople use these units all day long on the standard battery, then again, they arent working the machine the way audio recording would.