Zite is an awesome iPad app that offers a personalized magazine from web sources (an amazing variety of public RSS feeds from conventional news to popular blogs). You start by giving it some keywords that characterize your interests. Then, every time you read an item, you can indicate whether you like it or not, and it will learn your tastes and give you more suitable content.
I love it, but I don't have my iPad anymore. What similar applications exist for the Mac desktop, or as a web app?