Andrew Carton of Treonauts published a good summary of RSS reader options for Treo 650 users. The headline readers include PalmOS applications that have paid licenses, browser-based RSS readers that are free, as well as email and Java-based offerings.
Of the RSS readers I’ve tried so far, Bloglines Mobile (part of Bloglines.com) is my favorite. However, if I was more into podcasting, I’d probably be using QuickNews. QuickNews has robust RSS attachment support, which means it can do things like download podcasts directly to an SD card installed in your Treo and play them in Pocket Tunes.