3 texts on free culture, intellectual property, remix culture, media democracy-- Lawrence Lessig's Free Culture, Dan Gillmor's We Media, and Kembrew McLeod's Freedom of Expression-- are all available through Creative Commons licenses, which allows them to be shared. These books are worth purchasing, but being able to have them on your computer or PDA to read also is a great bonus. Off the shelf has posted nice Palm versions of these. I've only skimmed the recently-released McLeod book so far-- but it looks great. It was already high on my to read pile, but having it with me on my PDA will probably help get it read even more quickly than its place on my queue would have otherwise dictated.
I read Lessig's back when it came out last year (in actual bookform), and downloaded a different PDA version of it at the time as well. But, if you never read Free Culture, please do so NOW! (whether in digital-- be it PDA or PDF-- or paper format). Seriously, do it.