The two gauges I used display the Coolant temperature and oil pressure (I never liked how new cars did away with the analog gauges for water temp and oil pressure).
These particular gauges (Autometer pro comp) have a logic output so that you can take setup warning lights when the temperature gets too high, or oil pressure too low.
I have them hooked up to a few LEDs that run along the perimeter of the LCD display (you can see the red lit up since my engine is not on, and the oil pressure is at zero)
And lastly, the phone mount in the center of the dash provides a convenient location in case I need to use GPS or to just take calls (using a Kinovo bluetooth interface)
The mount is simply the belt clip that came with my phone case, riveted onto a piece of ABS plastic.
Coolant temperature, and Oil pressure gauges: