Sanyo Eneloop LSD* Rechargeable Batteries are the only true choice, not only for the photographer, whenever AA or AAA batteries are needed. During the first half of my life I always used cheapo and not so cheapo standard rechargeables. Since I do not use them regularly, but only then and there every few months, I always ended up either with a set of trashy batteries or at least batteries that need a 3 or 4 day refresh run to return to "normal" capacities. So I learned my lesson. Don't ever buy anything else than Eneloops. They aren't even more expensive than other rechargeables.
 
Since summer of 2010 there are lame old and advanced new versions of the Eneloops available (just kidding here, the old ones were already great, but the new ones are even better):
 

	AA (LR6 mignon)				AAA (LR3 micro)
	HR3UTG (old)		HR3UTGA (new)		HR4UTG (old)		HR4UTGA (new)
Max. Recharge Cycles: Min. Temperature: Capacity after 1yr.: Capacity after 3yrs.: Technology: Voltage: Min. Capacity:	1000 -10°C 85%   Ni-MH 1.2V 1900mA		1500 -20°C   75% Ni-MH 1.2V 1900mA		1000 -10°C 85%   Ni-MH 1.2V 750mA		1500 -20°C   75% Ni-MH 1.2V 750mA

The models above are all white, special versions available in color.
 
Since Photokina 2010 there is an additional high capacity XX battery in AA size announced/available, which offers a min. capacity of 2400mA, but only 500 recharging cycles at max. Capacity after 1 year of no use is given with 75%. These come in black. Prod.-Code is HR3UWX.
 
Asian markets also know Sanyo Eneloops in size B and C, but until now these are not available in Europe or the US.
 
*) LSD abbreviates Low Self Discharge

La Crosse RS700 aka Voltcraft IPC-1L aka Techno Line BC700 etc. are high quality rechargers with a great set of functions. They offer 4 charging modes: Charge, Discharge, Refresh & Test. Refreshing will charge and discharge the batteries until their possible peak capacity is reached (good for treating memory effects). All charging modes are possible with 200, 500 and 700mA. The chargers have an LCD showing the mode, voltage and capacity as well as charging power and time for each of the slots. Each battery slot can be configured individually, but it's also possible to control all 4 slots simultaneously. The power adapter takes every voltage between 100 and 240V and has an exchangeable power plug to fit every wall socket standard of the world, considered you have the right plug at hand (usually there is only the regional adapter piece included with the package).
 
 
There is only one drawback here: The device is microchip controlled and will only activate a slot, when a battery is recognized. Fine so far. But if you try to load in a battery with no capacity leftover at all, like it happens with non-LSD types quite often, it will not be recognized and thus not be recharged. I'd think that this can't happen with the Eneloops, so just stick to them. But if you do have also other types of rechargeables, you will need a standard cheapo recharger from time to time to put some basic capacity to the battery first and then switch to the RS700.
 
For people who can't get enough there also are the even more powerful La Crosse RS900 (aka IPC-1/BC900 ... adds 1000mA and 1800mA charging power cycles) and La Crosse RS1000 models available (adds 1000mA, 1500mA and 1800mA charging power cycles), but keep in mind that for most rechargeables treatment with more than 500mA will not be optimum and should be considered only for the few really important emergency occasions.