A spotlight will allow you to see many interesting things on the rock cuts and off in the thules. I recommend a light with a halogen bulb, rather than a sealed beam, as they generally hold up better and don't break the filament as easily. The pigtail adaptor is helpful as it will allow you to run the light directly from the battery. I have found the ones at K-mart to be better and less expensive than the ones at WalMart.
I prefer the 6-volt flashlight of this type to a regular flashlight, although many herpers have had good luck with a D-cell type flashlight. I like a wider beam.
Spare batteries and bulbs are a must. I have missed animals because my battery went dead while I was in pursuit.
Some other lights which have proven OK are krypton bulb bicycle lights, multi-cell D cell lights, and others. I like a light with a uniform beam and a spread of about 30 degrees. Try to avoid lights with a dark center. Try to avoid any "bright spots", as your focus will be drawn to that spot.

Insects can be thick, and a spotty or dirty windshield is a major irritation when road cruising. Some nights it will be necessary to clean the windshield three or four times.
The rain-X is a marvelous product. If it looks as if you may encounter some rain, apply a layer to a clean windshield. It is terrific in a drizzle, as you may not even have to use your wipers. However, it is a downpour when this product really proves itself. With rain-x applied, I have driven through downpours where vehicles were pulling off the road because they couldn't see, and I have not even had my wipers on.
This flourescent light is manufactured by Davis controls. Although there are other and cheaper models available (some as low as $9.00) which are acceptable, I prefer this type as it throws off a better light than other flourescent lights I have tried. I prefer the shorter "quad light" to the longer single bulb models.
n.b. Davis controls has changed hands and is know known as Suntech, Inc. of Chicago, Ill.
The battery is a 12-volt, available from a number of sources. The battery pack is a fused type from Davis Controls, but some people use other types or make their own.
Since the flourescent lights throw off a wider, more uniform beam than flashlights, they allow for better use of your peripheral vision. Sometimes a snake will drop into the grass. With a flashlight, I have been unable to find some of them. Once I looked for one for several minutes and the went back to the car and got the flourescent light. I immediately saw the snake about ten feet from where I had been looking, starting back up the rocks. The flourescent lights are excellent for field collecting and walking. They last 5-6 hours on a fully charged battery.