I was considering a Visor, but then I came across the TRG-Pro, and it seems to have the Visor trumped in memory and expandability. It is a Palm IIIx with 8 megs of RAM, and a Compact Flash slot. Costs $329, for an extra $80 expandability seem better than the Visor.
Also, another possibility which I just discovered.
Outpost is selling a Palm IIIx for $200 using a $40 mail in rebate. I think the Visor is still more worth it, assuming it works...