If you're talking about AA batteries, look for those that are 2500mah. These have the highest capacity so should last much longer than the cheaper ones.
Don't know where you live so not sure what brands are available in your area.
When you do buy these batteries, make sure you buy a recharger that supports such high capacity batteries, otherwise standard ones will only do half recharge... typically upto 1300mah.
There are 2 new types of NiMH batteries on the market.
-They have a 12 month shelf life and higher capacity.
-They work with any standard NiMH charger.
-Costs are higher than standard NiMH but should go down. Shop for price. I was surprised that Ritz price beat Circuit City.