Handspring Visor was THE BEST. The cartridge expansion ("Springboard" slot) was great. The unit was relatively affordable to begin with and was easy to tinker with. Once I had gotten it online by a series of like 3 or 4 cables and adapters from Handspring to my Motorola Startac, connecting to the GPRS network. It wasn't fast, but for simple text applications (email, AIM, etc) it worked.

Also I had an uber powerful IR Blaster (that could also learn any remote) that was great for terrorizing my father. Good times.