Nickel Metal Hydride
These are my personal favourite batteries right now (though I'm looking into Li-ion and LiPo)...html) Nominal 1.2V, and the discharge curve is nice and flat. You can draw a decent amount of current off them. Seem to be getting cheaper and more available (e.g Energizer at Target). I find these much more convenient than alkaline since there's nothing to throw away and no trip to the store before a trip (just need to remember to charge them). Theoretically they self-discharge, but I've used packs months after say Halloween or BM and they still had plenty of juice. I use a Maha smart charger... so far, so good. - mang.