It happened to me today. Same thing, exactly the same. I got a Sipik SK68 from DD with a pack of half-empty 14500s. I tested first with my cheapest of the cheap non-rechargeable AAs (wow, cool flashlight!), then with my empty AA (i have to throw away these rechargeables ... ok, I'll try charging then one last time), then with the half-empty 14500....
And the rest is history. :)
It's REALLY bright. So bright that zoomed in it is brighter than my only XM-L (Ultrafire V6-T60). Ok, the cell in V6 is probably half-empty or more. But who cares.
I can't stop turning it on every few minutes. :)
+1 for 14500s. It's worth trying them out, you probably won't regret it.
Viktor
Edit:
The cells at DD: UltraFire UltraFire 14500 Battery 3.6V 900mAh
and the Sipik at DD: SMALL SUN SIPIK SK68 3W LED Focus Cree LED Flashlight (1 x AA Battery)
This Sipik works with 14500s, at least mine does. :)