I've been using the Sanyo 2700mAh NiMH, and was getting some very good scanning times with them--much better than the stock batteries. Not sure if I had a bad batch or what happened, but of the dozen cells that I bought--I only have 8 that continue to hold a good charge--the other four won't hold a decent charge, and I've had to pitch them. Not sure what the reason was--I charged them on soft charge in a Maha charger--rotated them often, and even conditioned them every two or three cycles. Oh well... the ones that are left are still great batteries.
I ended up buying some Duracell 2650s--they are only slightly less potent--but every one of the cells that I bought still holds a good charge--not one bad cell in the bunch. In that respect, I feel better about those batteries than the Sanyo cells.
I've been using energizer 2500mAh with great results. They last a long time as long as you charge them slowly. I believe quick chargers ruin the batteries life cycle. Wally world has 4 for $10 compared to radio shack brand 4 for $20
I have been using duracell 2500, you can find them anywhere. They have been holding up pretty darn good. Use them in a Maha 8 cell charger. I have had some energizer 2500's and they dont seem to last as long.