There are quite a few sci calcs, so I'd suggest doing a search on www.pocketgear.com.

As for games, we have over 100 PPC games reviews on this site, so check 'em out

Warfare Inc is pretty hot (RTS), and so is Everquest and Age of Empires. There are plenty of action games as well.

For pay-for ebooks, I think most folks prefer Palm Reader eBooks from palmdigitalmedia.com. There's a PPC version of the reader, so have no fear. The prices are good and their DRM scheme isn't overbearing. For free ebooks, check out Project Gutenberg http://www.gutenberg.net/index.shtml and the Univ. of VA site http://etext.lib.virginia.edu/ebooks/

MS has an SDK that you can use with Visual Studio for C++. Don't know where they keep it these days but it's free and about 100 megs to download. Check www.pocketpc.com or the main MS web site.

Most all apps come in trial versions, so you can see if you like them before you buy.