Opera has a huge base of user scripts available for use, which allow users to add additional functionality to the browser, the user scripts are pretty similar to Greasemonkey scripts for Firefox.

Considering how popular User JavaScript are in Opera, there are bound to be several useful ones which you must definitely try out, and to help users out, the Opera Watch has put up a list of the most useful User JavaScript for Opera users.

The list includes several useful scripts like;

• Autosizer A script that will enhance image viewing in Opera, allowing you to resize images to fit screens and so on.
• Clean URI A script that auto-detects redirect URL and changes it to the direct URL
• Cooliris alike Preview links in current browser window.
• Power drag Adds ability to resize textareas, select boxes, iframes, objects, images and input fields.
• Linkify URL Makes text URL’s clickable, you may also want to check add-ons that convert plain text to links in Firefox.
• View Selection Source -  Allows users to view HTML source of only the selected area on the page.

These User JavaScript’s are definitely worth trying out. If you are new to User JavaScript in Opera, take a look at a tutorial on How To install user JavaScript it Opera.

Useful User JavaScript for Opera [Opera Watch]