I prefer low-discharge (LD) NIMH because:
-after sitting on a shelf for 12 months, they retain about 80% power, unlike regular NIMH which rapidly lose power
-they're rechargable and yet acheive performance close to that of more expensive lithium (e.g. Energizer e2)
-they're offered in AAA through D sizes, maybe more
-better regulated output in high-drain devices
-you can get six AA's, 2 AAA's and the charger for under $20 after $5 rebate @ walmart.
For brands, I like Rayovac Hybrid LD NIMH, although I've also heard good things about Eneloop LD NIMH.
-have a super-long shelf-life (like 10+ years, longer than alkalines)
-are higher powered than NIMH
-are lighter (some flashlights will float if you put lithiums in them)
-have some advantage as far as not discharging some kind of gas which most or all other battery types emit (I'm not sure on this one).
There are also rechargable lithiums. I don't know much about these, although it's the kind of batt in most cell phones. 123A is a particular size lithium battery that is frequently used in high drain devices. There are many brands of this size, at very different performance levels and prices.
-are appropriate is if you're putting them in something very low drain, like a TV remote or a digital clock.
What size battery do you need (i.e. AAA, C, etc.), and is it for a laser or is it for some other device? It would help if you shared some information about what you'd like to do with batteries.