Might I suggest http://www.bestbatt.com/default.asp. I've bought batteries for my Panasonic and Nikon DSLR there. They are generic labeled, but I've never had an issue with any of them and they hold a charge as well as the factory OEM's.
If you're using AA's, you might check into Eneloops or one of the other similar rechargeables. They last quite a while in my Nikon flash and it pulls way more juice than a camera.
If you get rechargeables, invest in a good charger like a Maha, as they won't abuse your batts.