Morry: google is your friend on this one. Like exploding powersupplies with computers there's plenty of documentation spread around.
Shadow - try to find out if any of those lights are regulated, so that brightness is constant rather than varying with remaining battery charge.
Fenix have just launched an 18650 light, btw. It will cost more, but their quality is usually excellent.
Oh - and never leave an 18650 on charge and go out of the house or where you can't supervise it. Not if you're using a made in China super-cheap charger and cells. There's a slight risk of fire. High quality protected cells and the Swedish Pila charger cost more but are safer.
They're all regulated, I'm just learning towards SB's romisens because of the respect for their stuff around the web and the fact that it's making significantly less ludicrous lumen claims. It helps that one of SB's mods was to add the same XP-G R5 that the Fenixes use.
The 18650's are more problematic though. I see why AW/Wolf and the Pila IBC are recommended so highly but the price of the Pila and the flashlight alone, without any batteries, is in the $80 range which puts me at the "oh just get a magicshine" level. Knowing these little bastages need so much special treatment instead of being more readily chargeable puts me even at my cheapest option I'd feel safe with around the price of a cygolite Hi-flux II off amazon.
I'm posting in the "best headlights under $50" thread for a reason. My little walmart Zefal's great for being Mr. Blinky but just absolutely does not cut it for pothole and root watch duty at 1am. I'm plenty comfortable macgyvering things, I've made my own RS232<->TTL converter circuit before, but those tend to add at least six pounds to your bike.
Gotta love how prices sneak up on you like this... I wonder if there are any comparable NimH options, they tend to be much cheaper on the battery side.