I am looking for a device to be used with a Pokeys57CNC board for the analog inputs for Feedrate and Spindle Speed Override. Any suggestions? Any Gotchas?   I am following the Tutorial on the PoBlog but have not seen a particular device specifications mentioned. 
Thanks, Jim

Analog inputs are available for this purpose - voltage range is 0 to 3.3V.

In Mach4, the analog inputs map directly to registers, that are accessible via LUA script to do anything. There is a blog article on how to use it for FRO.
In Mach3, analog inputs can be mapped directly to DROs in the settings with selectable gain.

I followed your blog entry to setup an analog  input. The register files shows the changing values as I turn the pot, but the script gives and error pointing to the line I added to the PLc script. I have rechecked and I have the line entered correctly.

Any hint on debugging this/

Are your blog reports available to print? I would like to print them to have by my system in the shop.

Suitable remote-controller for Mach4 are still rare right now.
I did my own one, but with Encoders instead of Potentiometer to adjust the Spindle, Feed and Jog Speed Override.
The Controller Board is an additional Ethernet Pokeys board beside my main PokeysCNC controller.
It work quite good, but was a lot of development effort with the PCB and all the LUA code.