No hype here guys. I've been using POWEREX NiMH rechargeable AA batteries exclusively for 5 years now and wouldn't change for anything. I use them in my Canon 420EX flash and my iFP 300 series iRivers. There's NOTHING out there more powerful.
They are made by
http://www.mahaenergy.com and can be purchased in their online store. Another great distributor of their batteries is
http://www.thomasdistributing.com. They sell other batteries, but once you go maha you'll never go back!
Go read the Great Battery Shootout on
http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM. This article is packed full of information regarding the finer points of rechargeable batteries! It is a little dated and doesn't include MAHA's 2500 mAh or their new 2700 mAh batteries.