If there's one thing that shouts "cottage," it's beadboard. This classic grooved paneling is a perennial favorite, and for good reason: Not only is it easy to install, but it's a no-brainer for adding warmth and character to a bare wall, a blank ceiling or bland cabinetry. You can't go wrong by painting it creamy white, but it's also fun to add a hint of subtle color and distress it ever so slightly. 
Hot tip: Beadboard can be a strong addition to a room, so a little goes a long way. The paneling in this bathroom pops because of its texture, despite being in the background.