Originally posted by Marc Sabatella Note there's no such things as Li-Ion AA's, at least not in anything resemble a 1.5V format that you can use in a camera. There are plain *lithium* cells (sold by Energizer most notably) and they work quite well but are not rechargeable, so much more expesnvie long term. There are also about a dozen existing threads here and in the beginner's forum on AA batteries, but you already know everything you need to know: Eneloops (or similar "hybrid" NiMH cells) are the best option overall, but if you're OK with spending a lot more money and throwing away a lot more batteries, lithiums do perform slightly better.
Marc is certainly correct that over the long term the Energizer Lithium batteries would be more expensive (and generate more waste). However, depending on how much you shoot it might not be
that much more expensive. I got over 2100 shots out of my first set of Lithiums in my Kx. That was, however, with minimal flash/LV usage.
For what it's worth, I had intended on using Eneloops when I bought my Kx but have been using Rayovac Hybrids instead because they were on sale at Target a little while back for $5 with a cheap charger and $3 for an extra set of 4 (there was also a couple coupon involved). I'm sure they are as good as the Eneloops and a high quality charger, but they've worked fine for me over the 9 months and I would guess I get 500-600 shots (at least) from a freshly charged set.