Some cameras come with brand-specific rechargeable batteries. I just see it as a way for them to get more money out of me!
However, I do use regular AA rechargeable batteries in all my cameras now. (Like Energizer or Duracell or Rayovac). It's great to be able to have a few sets of 4 (what my camera needs) in the bag and then put them on a battery charger when I'm done. Saves TONS of money, too!
I also use rechargeables for CD players, Wii remotes, regular (TV) remotes and anything else that uses batteries.