I've got one of these: http://www.ebay.com/itm/2-52mm-White-Oil-Pressure-Press-Gauge-0-120-PSI-Digital-Blue-LED-For-Car-Truck-/160816957511?pt=Motors_Car_Truck_Parts_Accessories&hash=item2571700847&vxp=mtrSeems to work decently, though it's "danger light" comes on at 18PSI, and my truck runs 12 PSI at warm idle.
Probably not accurate to the PSI(especially not if you've got grounding issues, as these are one-wire senders), but definitely responsive enough and a good relative measure anyway.