Puresmoker's Protege.
Built like a tank. Small. Uses 14500 Protected batteries that last me over 8 hours and is really good looking!
Silver Bullet! 18650 battery last me about a day and a half easy! Beautifully built, awesome switch, tough as nails, simple, elegant design, just perfect in the hand, all around awesome!
I agree with everyone who recommended the Silver Bullet it is an awesome device (up to 2 days battery life at 3.7) AND a 6v option which for me lasts an entire day. But if you're only interested in 3.7 something smaller like the BB might suit your needs better.
does the BB use 14500's the same as protege?
Little Chuck if you want a smaller model with long battery life.
The regular sized Chuck if you want even longer battery life.