LiFe looks to be a great alternative to NiMH.
6.6v so you don't need a voltage regulator and great life and a self-discharge in storage somewhere between NiMH and LiPo. Downside is they cost another 50% over NiMH.
I'll probably be switching over my gas and glow models to LiFe through attrition when my NiMH packs peeter out.