I use the Sharp Zaurus SL-C3000. It's abit pricey but does everything I want.
Zaurus SL-C3000 review
There is also the sl-6000 that was being sold on Amazon a few months for about $400. I don't know if they still do.
Zaurus User Group has more info on the Zaurus.
There are also instructions on make homemade battery packs for the zaurus on the ZUG forums.