Here's a list of some portable devices (which consider energy saving, so you don't have to carried around batteries as weight as of the device itself).

Palm OS Platform US Robotic Pilot : The very first of Palm family Visor : The expandable Palm family from Handspring Click here to buy a Handspring Visor!

Small Note Platform Notebook Crusoe CPU-based Toshiba Libretto L series Toshiba Libretto L1 Toshiba Libretto L2 Toshiba Libretto L3 Toshiba Libretto L5 Fujitsu Biblo LOOX series Fujitsu Biblo LOOX S5/53(W), T5/53(W), S7/60(W), T7/63(W) Fujitsu Biblo LOOX T8/80(W), S8/70(W), T9/80(W,M), S9/70(W)