There are several newsreader apps for iPhone, but this app might have the others beat--at least in the ease-of-use category. Opening this app gives you a list of categories to choose from. Once you pick a category, you're presented with all the popular feeds that fit the category. We especially like the way this app presents feeds from a site with a ticker, making it easy to pick out a good story as it floats by.
iPhone link: http://www.feedmenews.net/