Another great set of LED's that I've started using for the FGP Thursday nite Dirt Crits are these ones www.ayup.com.au. (site seems to be 'down' at the moment)
For $395 delivered you get 2 sets on twin LEDS (4 leds in total) (1 for bars & 1 for Helmet) charger & 3 Lion Polymer batteries (2 x 3 hr & 1 x 6 Hr)
Quite adequate for MTB racing at night (maybe not fast downhill) & weigh almost nothing.
Another great Aussie product from Queensland, excellent customer service and delivered next day from ordering