Princeton Tec Pulsar II, Only 1/4 oz.
Don't be fooled by the miniature size. It's actually quite bright and it's less than 1/4 oz. (with key ring removed). Brighter than it's competitor because it has two long-life (12-14 hour) replaceable lithium batteries. Easier to change batteries than the competitor because it doesn't need a small phillips screwdriver. Just pry it apart. Unbreakable bulb, tough case, handy squeeze feature or use the positive on/off switch. Batteries included. Available at any photo counter.