I've had an Exposure Maxx-D for about three years now and it has been faultless. It cost nearly £300 and being the first generation Maxx-D puts out around 900 lumens on full power. Newer versions put out around 1200 lumens.
The battery life is excellent and the cable free design is a real bonus.
I wouldn't recommend getting one though.
On a whim a few months ago, I decided to try one of these:http://www.ebay.co.uk/itm/CREE-XML-XM-L ... 20c5013dc9
The promise of twice the lighting power for a fraction of the price was too much too resist.
It's now the only light I use off-road and so good I bought a second one as a spare.
The Maxx-D has been demoted to the road bike.
These Cree XML T6 lights are brilliant, but not without a few minor issues that can easily be sorted.
Firstly, the battery isn't waterproofed at all, so it's a good idea to wrap it it cling film, a plastic bag or a condom to keep it safe and protected.
Secondly the stitching on the battery bag strap wasn't great on mine. So a bit of additional needlework was required.
Finally, the beam spread isn't that well controlled. I bought one of these: http://www.ebay.co.uk/itm/Wide-Angle-Le ... 3a7fbbefe1
It transforms the beam into a nicely diffused horizontal spread which is perfect for those dark nights in the forest.
So for £25, a bit of stitching and a condom...
(but that's another story)