The UltraFire C8 U2 from here: C8-U2 at $16.50. It's a U2 running at 3.0-3.2A on a good battery, great reflector. Reviews: here1 and here2.
In the 2nd review, rdrfronty measured 871 lumens OTF!! I got one, it's very bright, great throw, running an EagleTac 3100 or Panasonic unprotected 2900.
You gotta consider this light in a short list for one of the best at/under $20.