Good upgrade option if sticking with surefire - SureFire 600/900 Series Forend Weapon Light LED Conversion Bezel Assembly

If you have something like a Surfire LM2 then you're dealing with 200 lumens of output. This gives you 500 lumens of output in the same footprint for not much cost. Now that said, there are now options other than Surefire, such as the Streamlight TL Racker. That will give you 1000 lumens of output and that entire accessory costs less than this. Your call.