I would use the packaging they came in, if possible.

Packs of 4 Eneloops normally come with a useful holder.

If you know someone that has some of the plastic .30-06 class (.308, 7mm Mauser, .270 and so on) cartridge holders, they work rather well.

Take 4 AA batteries down to your local hardware store to use as a guide and buy a piece of PVC or CPVC pipe, a glue on end cap for one end and a screw on end cap for the other. The store will cut the pipe for you and probably glue it up for you and you won't even have to buy glue. Between PVC and CPVC there is a size for every type of battery.

Batuca battery case

http://goo.gl/Ofr8e

or for 8 AAs

http://goo.gl/FfdLi

Found this at my local WallyWorld in the nutrition section. It holds some kind of protein shot, but I got it just for the container. I carry my cell phone emergency charger,a AA battery, and the Bic in it. The ubiquitous altoids tin holds six AA's with very little room for them to rattle.

This is the type I purchased on Ebay last year. It's versatile because it can hold AA, AAA, AAAA or CR123A size batteries and you can clip them together, they also come in different colours. They aren't waterproof but they do keep things organized and prevent short outs.

I've got a dozen or so to hold my stock of AA and CR123A batteries but carry 1 pack of 4 AA batteries in my daypack.