For discovering new web content, everyone knows StumbleUpon. NextStories is a cool alternative that presents pages and articles in a Pinterest-like interface, giving you more control over what you see next.
While StumbleUpon drives you from one page to the next, NextStories is all about giving you options. You don't even have to sign up for the service; just drag a bookmarklet into your bookmarks bar, and tap it whenever you're on a site that you like. A grid of related articles that you might enjoy will immediately overlay on top of the page, and clicking one takes you straight there. There's no menubar overlay, and no special sharing features or ratings; NextStories is strictly about getting you to a new article.
This refreshing minimalism does come at the expense of customisability. NextStories won't learn your habits and interests over time like StumbleUpon, but for just killing a few minutes on the internet, I prefer NextStories' simpler approach.