If you're using Firefox and you want to keep JavaScript enabled but stop auto-playing videos, you can go into about:config and set media.autoplay.enabled to false. I'm not sure if other browsers have a similar switch, but this works in any current version of Firefox. It only affects HTML5 video containers; Flash and Silverlight video containers may still auto-play.
I do this, but also be prepared for video you expect to play to no work as expected. For instance, a video might appear to be frozen or "loading" until you click on it.
