Check out sniper hog lights. They have several models that will mount right to your gun so you don't even have to have someone hold the light for you. Reasonably priced and EXCELLENT customer service as i have learned first hand. I highly recommend them.

for a light that is bright and small I would go with a surefire, however they are expensive, but can be upgraded with better bulbs and batteries, I would trust my life to mine though it has helped me through some pretty dark places.