There are more than 500 Opera extensions available for download. Out of them the following are my favorite extensions.
Snap Links allows you to easily open multiple links in background tab by drawing a box around them with mouse. Read more...
Automatically loads the next page and inserts into current page when you reach the end of the current page.
Shows an image preview popup when hovering over link that points to an image file or a page with an image.
Shows translation of text in a balloon near text with one simple click.
Add CSS to any website to change the look and feel without creating a CSS file.