If you really need something small, I used a Fujitsu LifeBook 4 years ago. Check sites like http://www.tuxmobil.org
for user reports on what hardware works well with which distros.
Otherwise, I find the HPs very nice and have no problems with anything but the WinModem (which I don't use anyway). You might do some research on accessories - years ago I used a Toshiba and one accessory was a battery the size of the computer - 11 hours play time. Otherwise see if 'Targus' (or was that 'Targa') have a suitable adapter: DC
C for car battery or for aircraft use. One 'accessory' for the HP is a battery with a much higher capacity than the one provided at sale; I can't remember how much longer it's meant to run thoguh.