Looking for something a little different? How about an infrared flashlight. This 12 LED flashlight emits a beam of invisible infrared light. All you need in order to see the light is a camera capable of viewing infrared light. Most expensive DSLR cameras have a built in IR filter that prevents them from seeing infrared light. iPhones also have filters that prevent them from seeing infrared light. Cameras that have a "nightshot" or night vision mode will easily see infrared light.
Why would a geocacher need infrared flashlights? It turns out that some materials are opaque to white light but will allow the longer wavelengths of infrared to pass through. You can use this fact to hide coordinates such that they are only visible when viewed with infrared light.
You won't need these lights often but you'll be happy you have one when you do.