Popular Photography magazine's website has published a useful comparison of AA batteries, shopping around for the best prices, by spending $200 that bought seven sets of rechargeable and seven sets of single-use batteries -- 84 batteries in total.
The results for the rechargeable batteries were somewhat ambiguous, but Pop Photo chose the Energizer 15 Minute Charger as the best buy, while the Energizer e2 Lithium batteries are the best buy for single-usage batteries. As you'll see from the comparative data, there are many ways to determine the results.
For the in depth comparison: Pop Photo Batteries' Test
