Remember my post about ordering a backup battery for the iPhone (works with all iPods, though)?
I like it. Works so far. Lithium-ion rechargeable, very small, and is supposed to last for 300 cycles. If you’re not an idiot and use this only for long trips…well, that should last you at least three years, which is worth the $50.
See the original post for the link, but it’s still at http://www.richardsolo.com, I believe.