Try something like the electron 10+5W (Halogen). I got mine from CRC for £40. I have used it a couple of times a week for the last year. They are fine for most types of riding, except full on downhill into the unknown!
I have a friend who has bought the Niterider Minewts (LED). They are great, but don't justify the extra £100. They aren't much brighter than mine, and they dont last that long I don't think that the LED technology is quite there yet. Give it a year or two.
I've got the Electrons that Carl mentions. They're OK but I felt I needed just a bit more so I've just got a Silva L1 head torch (3W Luxion LED) from Above and Beyond for 56 squid and it's ace in combination with the Electrons - don't need owt else!