USB to GPIO module
Perhaps the simplest solution to the stated requirement is the FTDI FT245R IC.
The key points of note in the context of the question are:
- Royalty-free USB drivers from FTDI for Windows, MacOS and Linux (MacOS support only for USB VCP mode)
- Complete USB device mode protocol handled on-chip without custom programming
- Complete USB hardware on-chip, including USB resistors
- 8 GPIOs available - will allow future expansion for inputs from the microcontroller too
- USB suspend / resume support, to switch device to low-power mode when not in use
- Integrated level converter and 5 V, 3.3 V, 2.8 V and 1.8 V totem-pole output, so it can talk to most standard microcontrollers
- No additional crystal or oscillator required, it's all integrated.
- Free sample implementation code for both computer and FT245R ends
In terms of time saved in implementation, and future requirement bloat, this is perhaps the fastest, simplest and cheapest 1-chip answer to the requirement. Price for individual units is around $4-5, and in the $2 range in volumes.
This adafruit micro-usb to GPIO looks good, but the Numato one you were talking about is a bit bigger for a bit more. If you're really looking for something big and you're willing to pay some more money, the biggest Numato variation is for you.
Anyways, I'm getting the adafruit one mostly because it's very small, which is what I need for my project.
(The biggest numato version is here: http://numato.com/32-channel-usb-gpio-module-with-analog-inputs/)