I was at a gem and mineral show today and ran across a rechargeable battery technology I had never heard of before. The NiZn 1.6V batteries are fairly new, though they've been around longer than I would have suspected.
At 1.6V these AA and AA batteries are a lot closer to the voltage of the equivalent 1.5V alkaline. The vendor whose table I saw them at uses them for his UV light (used for examining fluorecing minerals). These lights won't run with 1.2V NiCad or NiMh, but they work just fine with the 1.6V NiZn batteries.