Click the Headline for Keepvid.com
If you see a youtube video you'd like to have for ref. Or to play with in your own aftereffects project.
Copy the youtube url, paste into keepvid. It even gives you the option of different resolutions
If you're watching youtube and want to real time watch a higher rez version, add
at the end of the url and hit enter. If there is a high rez version it will play.