Chrome only: Google Chrome extension Chrome Reader subscribes to RSS feeds in your Google Reader account with a single click, and even changes the icon for sites you've already subscribed to.

Once you've installed the Chrome Reader extension, you'll see a new icon in the location bar—click the icon once to subscribe, and optionally add to a folder, and once you've already subscribed to a site, the icon will change to a blue Google Reader icon to indicate that you're already subscribed. If you're both a Google Reader and Chrome user, this extension is by far the easiest way to build your subscription list without clicking through a number of times.

Read more: Subscribe to RSS Feeds in Chrome with a Single Click