Costco has the Eneloops at a very nice price for 8xAA's and a charger plus it comes with some AAA's and adapters. Bargain price if you're looking to buy into some rechargables...
I shopped for rechargables recently. Eneloops at Costco were (by far) the best price I found -- FYI if there's one near you.
For NiMH batteries consider low self discharge, especially if you don't use them frequently. Sanyo eneloops and other brands have low self discharge batteries. You charge them, leave them on the self and they still have a large amount of capacity a month or two later. Normal NiMH batteries will drain much faster. See www.thomasdistributing.com or www.candlepowerforums.com. I have no association with thomas - just a happy customer.
One important thing to consider is your use. If you shoot with flash only occasionally, then the investment in rechargeable batteries may not be worth it, when you figure a few sets plus a good charger. While the technology has certainly improved, when they sit, they loose power at a greater rate than alkaline batteries. So, if you use your flash only occasionally, then I would suggest sticking with good alkaline batteries. You'll waste more time and energy charging and recharging (that's lost to sitting, not use) than you'll gain by going to rechargeable batteries. They can be great - but it depends on your use. In my experience you should be using them regularly, for chunks of time, before making the investment.
At one point I had a camera that would use NiMH batteries and I have four or five sets plus a good charger. Wasn't cheap, but it was the way to go and worked well for me. When I was shooting and out of power - I would pop in a new set - then recharge at the end of the day.