Photographic Gear Needed
Camera Selection - A digital SLR will work best although a point and shoot will be able to capture a few shots (provided you use the camera's flash or a tripod). With an SLR or other camera with manual control, you will be able to control
Lens Selection - With an SLR, you have a variety of lenses at your disposal. The ideal lenses for cave photography are those with apertures of F/2.8 or faster. My top four lens picks would be as follows:
Ultra-Wide angle zoom - A fast wide-angle zoom lens (like the Tokina 11-16mm AT-X DX F/2.8) on a cropped-sensor camera will allow you to capture the most area in the tightest of spaces while keeping the aperture as wide as possible for a zoom lens (F/2.8) to maintain the shortest exposure time possible. Even without a tripod, you should still be able to sufficiently hand-hold a lens like this as the ultra-wide angle zoom is less susceptible to camera movement.
On a full frame camera (Nikon D700/D3, Canon 5D/1Ds, or Sony A850/A900), a 14-24mm F/2.8 or 16-35mm F/2.8 lens is recommended for Nikon shooters and Canon/Sony shooters respectively. The Nikkor 14-24mm F/2.8 is renowned in its sharpness and ability to capture stunning images. Likewise, Canon and Sony both have superb L and Zeiss Alpha glass to cover the ultra-wide shots. These lenses may seem awfully expensive, but they help you make the most out of your full frame's sensor size and megapixels.
Standard Zoom (Preferably F/2.8) - This is the one lens you cannot get away with because it will cover some of your wide angle and more intermediate focal lengths when needed. The good news is that you probably already have one that has at least F/3.5 at the widest end.
Fast Prime (F/1.8) - A lens with a bright aperture will help you capture as much light as possible in the shortest of shutter speeds. In combination with a high-ISO, you will be able to virtually "see in the dark." A 50mm F/1.8 lens is cheap and easy to come by. They are also decently sharp and make a great addition to anyone's budget kit.
Macro - This lens is optional but as a macro shooter myself, I would never pass up the opportunity to get some closeups of cave formations. With a macro lens or macro function on your point and shoot, you will be able to pull out some incredible details. It is also particularly useful in low-light situations as they have apertures of F/2.8 or wider.
Flashes/Strobes - A couple flashes should be plenty. Even with one flash you could get some neat effects.