Have been using the IXON IQ for a few years now, for batteries, I use Energizer Lithiums, they can be picked up on eBay for not much more then regular batteries (at lease in the UK), and last much longer than regular Alkaline batteries.
Have tried the fork mount, and didn't find it much/if better than the handlebar mount for beam.
If your looking at re-chargeable, would discount the ones that
#kingston links to, as these are only 2000mAh, which is pretty low spec for today, would look for around 2500mAh, Sanyo Enloop are a good choice if looking at high capacity.