Costco visitor here. Those 48 x AA packs for about $9 or $10 are great!

I attempted to standardize batteries a while back but gave up. I try to keep lots of AA (alkaline + lithium), AAA (alkaline + lithium), and 123-sized cells (lithium) on hand.

You're also gonna need a way to keep batteries together and protected. Here are a few web sites with cases and whatnot:

http://www.inanycase.com
http://www.tadgear.com
http://www.countycomm.com
http://www.toolsaviation.com