I wrote a plugin for the Elexol boards. 24 bits of I/O via USB.
http://www.elexol.com/IO_Modules/USB_IO_24.phpThere is also the PoKeys plugin that Scott Shafer wrote. Pretty neat little device there.
And then any MODBUS device will work for IO. The Galil RIO, for example. Kenny wrote a nice tutorial on how to integrate one.
I downloaded the driver for and docs for that PIO-16/16T. The offer still stands for that if you like.
Steve