I have a couple, well a few older vehicles. I was looking into adding some gauges - oil pressure, water temp, etc. I got to thinking about just doing an Arduino board for this stuff. Maybe I'll grab some mpgduino schematics and modify them a bit.

A good set of Oil pressure, Oil Temp, Water Temp, Voltage gauges will add up to $75 easily. I can make a small digital version that would show those as well.

What other rover specific items would be useful? After my recent issue, I'm thinking fuel pump power would be a good one. (Just tap it after the inertia switch) Fuel pressure may be helpful too...

 

Trans temp, engine oil temp

If you are obd2 an ultra gauge will display any sensor reading iirc