Bookmark OS - Bookmark OS is like Mac or Windows optimized for bookmarks.
Raindrop.io - All your articles, photos, video & content from web & apps in one place.
Bookmark It - Create awesome notes on YouTube videos
Siimpl Bookmarking - Start collecting and organizing what interests you
Lynkmark - One place for all your bookmarks
Twitter Bookmarks - Create shortcuts to your favorite users/tweets on Twitter