I've tried a number of lights, but the best one is the Energizer or Eveready Contractor 2AA. In my area you can buy them at Autozone. One of my posts on this mod.
This light is cheap, durable, and has the best beam quality of 2AA PR lights that I've seen. The biggest drawback is that if you keep it on more than 1 1/2 minutes, the plastic reflector will soften and distort. You need to trim down the internal ribs and it also helps to compress the tailcap spring a little.
This light is even better with a Surefire P90 or P91 lamp in it!