http://www.byedesign.freeserve.co.uk/ -- this is an application called SpreadCE, it is better than the default excel app bundled into PPC OS.
http://www.softmaker.com -- these guys are working on a spread sheet app that will have no lost features in conversion, it isn't out yet, but their Text Maker app is probably the best app on any palmtop system, of any I've seen, it is a Word Processor with no file conversion, better than Word XP IMHO.
:)
Palm I believe has a better bundled app, but PPC has better 3rd party IMO, and that Spread CE is free.