The 404 error page is quite possibly one of the most overlooked bits of branding on a website. It's a place where an opportunity can be missed or made, and most companies (and designers) don't take the time to get it right. In 2012, Renny Gleeson gave a witty, fascinating, eye-opening talk at TED. In it, he describes the 404 page as an opportunity that we're all missing. It's only four minutes and four seconds, so have a watch.