One *negative* vote for the Petzl eLite.. I'm suprised this light always gets mentioned (I have one).
– it's not very bright at all, esp compared to new Cree LED based lights
– it's runtime is very short (runs on a couple of button batteries, what do you expect)
– it's unregulated, so it's discharge curve looks like K2. ie it's brightness starts noticeably dropping very very quickly.
– clumsy switch
Good lightweight handhelds are AAA based lights like the already mentioned Fenix L0D, I have the Liteflux LF2 which is a similar light but with programmable settings (and a fiddlier interface to go with it). Other good simple single-level AAA lights are the Arc AAA and the Fenix E01. With a single lithium AAA, all of these are of similar weight to the Petzl eLite, but *way* overpower it in brightness + runtime, and, unlike the eLite, all are regulated (so constant brightness).
Sadly there aren't many ultralight headlamps with decent LEDs. Zebralights (~2.2oz) are probably the brightest and lightest, it has a 80 degree flood, you might want more throw than this though. The updated Princeton Tec EOS II would be a good one, but it's hardly ultralight.