Petzl Zipka Headlamp - Not just for camping
I originally bought my Petzl Zipka headlamp for a camping trip, but it's also useful in a variety of other situations in which you want portable, hands-free illumination. Unlike most other headlamps, this one is extremely compact, since it has an ingenious retractable band. Note that I didn't say "headband" -- the retraction system maintains constant tension, so you can easily strap it to your wrist, a post (for fixed task lighting), etc.
I recently used mine during a scheduled power outage in my computer machine room at work; I had to do some work in the dark, and needed to use both hands, so this was perfect!
There's a newer Plus model, too; it's a bit more expensive, but has an extra LED and some other cool features.
Update: 2005.12 - A friend gave me the Petzl Tikka XP for Christmas. At first I thought, "Cool, but I already have a headlamp." That was before I switched this one on. It's not as compact as the Zipka since it uses a standard headband, but it's really bright, and has a "boost" button that kicks the brightness up a couple notches! Plus, it has a sliding diffuser, various brightness settings, and a blink mode. If I could have only one, the Tikka XP would be it, especially for camping, but the Zipka's compact size is really nice for travel, so I'm glad to have both.
Update: 2006.08.15 - REI used to carry both the Zipka and the Zipka Plus, but no longer seems to. The Petzl Tikka XP is still available.