[Al Skierkiewicz]

Dan,
The circuit Danny has included is standard protection for both inputs and outputs. Any voltage that exceeds the power supplyrail by more than 0.6 volts (the diode forward voltage) will be connected to the power supply rail. However, the diodes normally used, 1N4000 series, are usually too slow to allow really short and big spikes from getting through. There are several MOV devices that can really eat up the spikes (and are non polarized) available from Digikey and others. I recommend both solutions. You don't want to destroy the ADQ.