Handheld external display ideas for embedded device

Any experience using handheld external displays to enter/display data
in the field for an embedded device? Whats easist to get up and
running? RS-232 or USB communication ok, wireless less ok. I suppose
options off the top of head are PDA's, palm computers, smart cell
phones, gameboys,  or maybe they sell custom
display/keyboard/communication link only units for this purpose?

joep wrote:
> Any experience using handheld external displays to enter/display data
> in the field for an embedded device? Whats easist to get up and
> running? RS-232 or USB communication ok, wireless less ok. I suppose
> options off the top of head are PDA's, palm computers, smart cell
> phones, gameboys,  or maybe they sell custom
> display/keyboard/communication link only units for this purpose?

RS-232C or the more robust RS422 are commonly used.
You can also use a minimum IrDA stack with only the IrLAP
protocol if your embedded device has scarce resources.
RS-232C is certainly the easiest if your handheld device
has such a port.