http://www.copquest.com/10-6800.htm
Streamlight TLR-1: Great LED weapon light for $116.37
I ordered mine from this vendor and own two. Useful for most railed pistols, shotguns, or rifles.
2 x CR-123 Lithium batteries / 80 lumens...in practical terms, these lights will reach out about 35 yards in dark woods, handily cover anything from my house to the curb, and light up any possible line-of-sight inside of my house or yard.
I like having the LEDs as I don't wear PVS-14s at home, prefer the natural white light, and was specifically looking to get away from xenon/halogen bulb burnout and breakage.
The light is compact, lightweight, not overly expensive, and every bit as good as my handheld Surefires (and is comparable in performance to my issued SureFire 951).
I get the impression you are looking for a general purpose short range combat light for home defense (that won't break the bank). The TLR-1 will work just fine. I run one on my issue Beretta and keep the other at home for my personal AR. You can mount using Daniel Defense or Yankee Hill offset flashlight mounts which will put the controls right at your support hand thumb when using a vertical foregrip. Alternatively, tape pressure switches are available from the same site that sells the light. CopQuest is GTG.
You mentioned that you wanted long battery life and AA capability. CR123 Lithiums are going to last forever running LEDs and will not go dead in cold weather (unlike AA batteries). It's a consideration if you ever find yourself outdoors in the winter or leaving the weapon in a cold car.
BTW: I am issued SF 910A & 951 for my M4A1 at work. They are rather spendy. I also have a very powerful IR/White weapon spot that WILL illuminate out at 500 yards. It too is quite spendy ($2800+). I've been using most of the better SF versions for many years, but am very satisfied with the TLR-1.
There is a lot of junk out there for less than $40 and a lot of good lights for $250 and up. To date, the Streamlight TLR-1 is the only satisfactory LED weapon light I've found that delivers $250-$350 performance level for less than half the money.
Hope this helps.