Another vote here for the Sanyo "eneloop" low-discharge NiMH rechargeable batteries. Costco has been selling a pack with 8xAA, 4xAAA, C & D dummy cells, and a charger for about $25.

I've been really impressed with them and have been using them in my GPS and an old PDA with great results. Battery life seems to go on forever.

http://www.eneloopusa.com/

The downside? Now there are a lot of the Costco brand AA alkaline cells sitting on my shelf gathering dust.