I use rechargeable batteries for everything that I can, as divers we should be more concerned about the environmental impact of disposable batteries (mercury, etc). I have 2700mah NiMH AA batteries from Powerex, I also use 5000mah C cells from Powerex as well as some 4500mah C cells from Accupower.
As others stated, don't buy a cheap charger. Get one that is capable of conditioning the cells, I use a MAHA MH-C808M which has a LCD display showing the status of each cell. It can charge 8 AAA, AA, C, and D cells at a time. It has cell conditioning and soft-charge options. The nice thing about the LCD display is you can see when one cell has a problem, if its more "dead" than the others or takes significantly longer to charge. If you are trying to use a bad cell the device is going to lose power more quickly and suffer from possible under voltage problems on high draw (strobe recharge).
I order mine all from Thomas Distributing, I've had great luck with them and they give you cases for the AA/AAA cells. I have purchased some brands that totally suck though. Stay away from iPowerUS or Lenmar "NoMEM", I've had less than stellar performance from both.
My 5000mah Powerex C cells will power my UK C8 eLED+ for 5+ continuous hours submerged when I gave up on the test. They seem to tolerate the cold water well too, haven't had them go dead after multiple days of "night" diving (2-3 dark dives/day to to water conditions).