I recently installed a Dakota Digital ODY-19-4 air ride gauge on my truck.
ODY-19-4
It will monitor 2-4 bag pressures as well as tank pressure. I found that it's much easier to dial in the bag pressure with the digital gauge. It has the option of hooking up a warning light or buzzer to come on at a "low limit" that is user set. Also, if you hook a tail light or dash light to it, the display will dim when the headlights are on.
East to install. A little pricey in my opinion since you also have to buy the sending units seperate (one for each bag and one for tank pressure).