Google Reader (free web service)

RSS feed reader with numerous features, including sharing to other services, starring of interesting articles, and folders for feed sorting. I use this far more than any other web application, as I'm constantly reading things from across the web, and Google Reader is the best way of aggregating all the new content from many websites into one place and presenting it in an easy-to-read list, along with knowing how many new articles are there today and not missing a thing. I even subscribe to individual feeds from LW, such as particular users I don't want to miss comments from.