I do keep my batteries numbered in sets as Brian Auer suggested last week over at EpicEdits - not doing that really adds to the possible headaches of what's dead and what's not. Usually I pitch the set at the end of the evening, head to Sam's Club the next day and pick up a few more sets. A few months ago, I saw a couple of stories talking about these new Lithium-Ion rechargeables that hold their charge quite a bit longer and "memory" is not such a problem. Then I was cruising our buddies, 1001 Noisy Cameras, and saw they were selling several versions of the new batteries in the right hand column of their site. Not two days later, a review of the Sanyo Eneloop batteries over at Imaging-Resource. There's was quite a lengthy review with some very helpful reader feedback.
These batteries do seem to be the way to go for us wedding and event shooters. Hey, they don't break the bank, and they make a small portion of our lives a bit simpler - I would go check them out. Here is the Imaging-Resource review right here. Here is the 1001 Noisy Cameras link right here - just scroll down a bit, the batteries are on the right side.