I use a Q5 light for a helmet in conjuction with a P7 on the bars.. The L-mini is a good size for a helmet light..

http://www.shiningbeam.com/servlet/t...ni-1081/Detail

If you are looking for a small sized P7 with lots of driver options, there are some builders on the candlepower website making some nice modded flashlights.. The price is over 100.00 but you get exactly what you want in a very small form factor..

http://www.candlepowerforums.com/vb/...d.php?t=218409