I started with a Spectrum DX7 radio and receiver kit. It came with a garden variety 4.8v 4 cell battery pack for the receiver. With this battery I would get 3 or 4 ten minute flights before the battery level indicated a recharge was needed.

Someone at our club mentioned the Sanyo Eneloop batteries. I got one of them (they were maybe 25% more expensive than the garden variety battery) and I now get 7 or 8 ten minute flights (with a .40 class plane) and still have plenty of power left in the battery. I reckon they are well worth the slight bit extra they cost.