The Zaurus SL-5500 fits your requirements for hardware and software (SD and CF expansion; runs linux and java natively; hardware fully supported by OS) but it's battery life is nowhere near double digit. With a good battery, I've had about 3 hours of solid use per charge, or somewhere a little less than a week of just standby. Plus, it started at $400 retail, so now on ebay it's running at $100 for a starting bid, only to go up.
There's one on ebay now for about $165. If you're willing to go over budget slightly, that's a good choice.
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The Zaurus SL-5500 fits your requirements for hardware and software (SD and CF expansion; runs linux and java natively; hardware fully supported by OS) but it's battery life is nowhere near double digit. With a good battery, I've had about 3 hours of solid use per charge, or somewhere a little less than a week of just standby. Plus, it started at $400 retail, so now on ebay it's running at $100 for a starting bid, only to go up. There's one on ebay now for about $165. If you're willing to go over budget slightly, that's a good choice.