Watchkin is a free service that allows you to watch and project YouTube videos without seeing the related sidebar content typically seen on YouTube.com. Watchkin can be used in a few ways. You can enter the direct URL of a video into Watchkin to have the sidebar content removed. You can search for videos through Watchkin and have family-friendly results displayed (if a video appears that is not family-friendly Watchkin has a mechanism for flagging it as inappropriate). Watchkin also offers a browser bookmarklet tool that you can click while on YouTube.com to have the related content disappear from the page. In the video below I demonstrate how Watchkin works.
Applications for Education
The Watchkin website and browser bookmarklet are great tools for teachers who want to show a YouTube video in their classrooms without risking displaying "related" sidebar content. To be clear, Watchkin is not a work-around if your school blocks YouTube and it is not a tool for downloading YouTube videos. (Downloading YouTube videos is a violation of the YouTube terms of service).