Preferences > Advanced > Content. Uncheck Enable JavaScript to disable it globally.
Then when you want to manually enable JS for a single site:
Right-click anywhere on page> Site Preferences > Scripting. Check Enable JavaScript.
* blocking is the default, with whitelist enables
* quick script block for individual sources on a page; I can disable content from turner.com and revsci but can allow cnn.com when I am viewing cnn.com pages
* block is for plugins, too, and I can left-click the plugin image to selectively enable that specific plugin, whatever site it is from -- flash, silverlight, java, and other embeddings
* blacklisting sources per site or for all sites
* XSS protection
* weird script behavior protection, such as malicious attempts to overlay controls so that a user accidentally activates the wrong thing
* global override (allow all scripting temporarily)
* some cookie control
Here is a more comprehensive description: http://noscript.net/features
Maybe there is not a one-stop shopping for Opera, though, and I can get all this with multiple Opera extensions? I did run down a path at one point that made the JavaScript control more NoScripty, but the rest of NoScript's benefits provide a too-nice user experience and sense of safety.
Note: I am not a Firefox fanboy. I just really love NoScript's help. The only other real advantage I feel Firefox has over Opera is its JavaScript support (https://secure.wikimedia.org/wikipedia/en/wiki/JavaScript#Ve...). I periodically check to see if the next version of Chrome will support the hooks a NoScript clone would require, and Opera periodically grabs my attention.
There is a shortcut key for that - F12, so it's actually quite convenient :-)