It all depends on the size of light you're looking for but as the previous poster stated the options and quality will usually be better if you get the light of your choice and then purchase quality rechargables for it.
As for as a rechargeable battery format goes, it's pretty hard to beat the single 18650 with regards to its reasonable size, great capacity, and easy of recharging vs. lights using multiple batteries. I think lights that allow the use of the 18650 is a great place to start.