Astromist are currently beta testing there software for PDA users. If you find bugs and report them you can get a freebie later.
http://www.astromist.com/pages/download.html
Make it crash and freeze repeatedly and report it.
If I were to buy one application for a PDA out there it would be Tachyon, miles ahead of the competition. The next in like is Astromist and Starcalc
http://www.relex.ru/PocketStarCalc/
Regards