Hardware

DAP uses a turtle on their web page so it must be good!
Dell (Axim)
HP (iPaq formerly a Compaq product; and from before the merger, the Jornada)
NEC MobilePro
Symbol Technologies PDT 8100, PPT 2800
TDS (Recon, Ranger(formerly from At Work Computers))
Trimble (rebadged Recon, GeoExplorer XT)