Rechargeable Alkaline: Believe it or not, these things are still around. Most of you remember the now-discontinued Rayovac Renewal Recharageable Alkalines, but rechargeable alkalines are still available from Pure Energy and EnviroCell, among others. Here's what Michael Bluejay says:
Even the special rechargeable alkalines, like the Rayovac Renewal, have the same problem: very few recharge cycles, and ever-decreasing capacity.That said, there is exactly one circumstance in which charging alkalines might make sense for you:
You need the extra voltage an alkaline puts out. Some devices that take multiple batteries won't work with NiMH because the voltage is too low. (more on this problem) And with LED flashlights, even though NiMH will work, you'll get a brighter light with RA's.
For most people and circumstances though, charging alkalines is pointless.
Nickel-Zinc (NiZn): Startup PowerGenix has introduced their new line of NiZn Rechargeable batteries. As you might guess, you'll need their special charger to recharge them. Some folks really like them.
Lots of info on the internet. Start here.