Window Expander for Chrome lets you view YouTube videos in near-full screen without hacking Flash
There are ways to get around this by replacing specific Flash DLLs with tweaked versions, but really, who wants to mess with system files like this? Window Expander for Chrome is a far less invasive solution. It adds a button to Chrome's Omnibar which you can click to display a full-screen window with the video you're currently watching. Since Chrome has so little, well, chrome, it's the next best thing to full-screen. Window Expander is simple, and it works. Go give it a try!