I get asked this one on a frequent basis from people who are looking or a PDF program and I always recommend PDF Viewer. It's full of features and it's free but we recommend donating of course. In the meantime features include:
Native PDF on almost every Palm OS 5 device
File Browser to pick up your PDF file from anywhere on your card
Handles received PDF files from EMail, Bluetooth or WWW
Very small on-device memory footprint by moving the renderer to the card
"Find" support in your PDF files
Scratchpad and personal bookmarks
Support for links inside the PDF. There are many other features and you can download and get more info at the
Metaview website.
THROWAWAY- Tungsten E2 and Wifi Card, The first person that emails me can have it it 