If you prefer a belt case that the Axim slips into check out Nutshell. For a flip case I like Fortte because it will fit either the standard or extended batteries, plus it is a high quality case. You also can't go wrong with Piel I got one for my wife but she only uses the standard battery.
I have used the red cloth bag that my sena case came in to carry around my extra battery. I just bought a new digital camera that came with a plastic pouch for it's battery, but since I don't have an extra camera battery, I'm using that case for my extra ax battery.
The only metal case I ever had was a RhinoSkin for an Axim X5. I felt very uncomfortable carry it because it seemed slippery to me, but I am sure they have changed now.
However, as I said before, I love my Sena case.
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What one learns for oneself, one is less likely to forget.