I use a Surefire L4 which uses a 5watt Luxeon Star white LED.
Me too! 123's are kind of expensive so I purchased a pair of Li Ions (each cell is as tall as a pair of 123's) and I get a solid hour of light before it drops out of regulation.
The L4 can be had for about $145 ish on ebay.
The batteries and charger is about $100 from
J.S Burlys They pay for themselves quickly even if you get your 123's for a buck each.
Cheers!