After researching the various options I've stuck with Eneloops. There are higher-capacity batteries but there are downsides to using them. Eneloops are the best combination of price/capacity/reliability/shot-to-shot speed.
6,560 FLASH POPS LATER: The Results of "AA" Rechargeable Battery Tests http://photography-on-the.net/forum/showthread.php?t=677074
Why Eneloop and Powerex? http://eu.nkon.nl/waarom-eneloop-powerex