Remember that iPhone-only .Mac RSS reader Apple quietly introduced barely a day before the phone's release? After trying out nearly every iPhone web app launcher that has an RSS reader bolted on and even Newsgator Mobile for iPhone (since I primarily use NetNewsWire on a Mac), I have to say that the .Mac Reader (reader.mac.com) is my hands-down favorite. It's fast and displays RSS headlines in a very Safari RSS-like fashion, and it seems to cache better than most web apps I've seen, as it offers lightning-fast response when moving from an individual article back to the main list of headlines and snippets.
As a bonus, this .Mac Reader app doesn't appear to require you to be a .Mac member to use it, though since I am a member, I would like to hear from non-members on whether this assessment is correct.
If you already have a bunch of RSS headlines in Safari, or you use a trick like the NetNewsWire drag and drop one I just mentioned, the iPhone's one-two punch of Safari bookmark/feed management and the .Mac Reader could be a great way to bring your favorite feeds on the go.