RepRapTouch is a concept to integrate a touch screen LCD with RepRap printers.
You can get color LCDs with touchscreen controllers (SSD1963) in reasonable quality from china off eBay - something like 30 USD for a 4.3" LCD and 40 USD for a 5.0" one.
RepRapTouch consists of a separate AVR Microcontroller which handles:
- Taking user input, building the screens
- Talking to the electronics via serial
- Print from SD Card attached to the display controller (most of those displays come with a SD Card slot) or from the SD Card on the main electronics Needs investigation if and how that's possible. G20 lists sd card contents.
- atmega1284p (128k flash, 32 I/O, 16k ram) That's the only big AVR I got laying around for testing. Probably an AVR with integrated USB will go in later)
- Is another arduino suitable?
- Connector to those displays (do they follow any pinout standard, or do we need adaptors?)
- The UI needs to be scalable, so that we don't need to reinvent the wheel for different resolutions
- Why a separate controller?
- Graphics display takes quite a bit of CPU time and interrupts for touch aquisition. The main electronics are busy with printing, and the firmware shouldn't become more bloated than necessary.
- What makes a color touch LCD on a 3D printer useful in 2016 ?
- See the discussion for thoughts on the interest of such a device in 2016. 
This is definitely inspired by Marco Antonini's RepRap Touch TFT LCD
The site seems to be down, but there is a bit of information on his project on thingiverse