www.lightmalls.comI would be looking at something like this;
http://www.lightmalls.com/red-color-sol ... 50-batteryAlso get a big battery as a spare.
Personally, I would avoid the large multiples of LEDs they will absolutely destroy the battery life. I think the run time on a 3* T6 or U-2 is under an hour on full whack, let alone a 6 or 7 LED light! Plus night riding is all about the change in lighting conditions anyway (within reason!)
A single U2 is more than bright enough for riding pretty flat out XC. I would consider getting a helmet and a bar light though. A flood light for the bars, and a single spot for the helmet.
I've had stuff from Lightmalls before, and would recommend them, they aren't particularly speedy (they come from Hong Kong) but I think they turned up within 2 weeks.... In fact I may well order the single U2 light and large battery soon...
Very tempted by the above light (not that I need another one....)