sfischer,
Welcome to CPF!
When you say "brightest" do you mean greatest total output or longest-throwing? The two can be very different depending on beam dispersion angle and type of reflector or lens. It will help us to answer your question if you describe the beam you're looking for and the intended use of the light. I can't immediately come up with a superbright rechargeable LED, and you may have to settle for a nonrechargeable. It is likely that the brightest LED light will be a "mod" (modified flashlight) created by some of our gifted CPF modders, rather than one that is commercially available.
Brightnorm