JavaScript considered harmful

http://www.scmagazine.com/web-20-attack-of-the-javascript-malware/article/113132/

http://www.blackhat.com/presentations/bh-usa-06/BH-US-06-Grossman.pdf

IE:
http://img208.imageshack.us/img208/5228/noscriptd.png

Firefox:
https://addons.mozilla.org/en-US/firefox/addon/noscript/

Opera:
It's one of the config options you can set per site.

Chrome, Safari:
You're on your own. Google don't want you turning it off, because they think it should be mandatory to stuff ads and all kinds of other shit down your eyes. Apple also think similarly, but more because they want things to "just work".