Chrome/Firefox/Safari: If you're tired of all the distracting, annoying content surrounding your videos on YouTube, you can hide them with simple browser extension Clea.Nr.
Clea.Nr overhauls the entire YouTube interface, making it simple and minimalistic: your video's search results are clean and uncontaminated by anything else, and your video plays in the centre of the window without anything else around it. You can dim the lights around your video, which is nice, and click a button to show comments and related videos. That way, if you want to still use YouTube's other features, you can, but can get them out of the way when you don't. It's actually a really welcome change.
Clea.Nr also has the ability to make Amazon's interface similarly minimal, but it's less helpful since instead of removing ads and annoyances, it removes a lot of the things that make Amazon useful, like advanced searches.
Clea.Nr is a free download, works in Chrome, Firefox and Safari.