An Arrow from the Sun

UserJS is an Opera feature that allows you to enhance the browser experience/a specific website by using java script. Scripts are often really small and quite easy to write. If you have not used UserJS before I highly suggest that you start with these scripts and see if you like them. Read Opera's quick introduction for more details :

autosizer http://userjs.org/scripts/browser/enhancements/enhance-blockquotes
Automaticly resizes images to fit the screen, can also be used to zoom in on a image

enhanceblockquotes http://userjs.org/scripts/browser/enhancements/enhance-blockquotes
Enhances block quotes Pretty straight forwarded

googlesuggest http://userjs.org/scripts/site/enhancements/google-suggest
Adds Google suggest (http://www.google.com/webhp?complete=1&hl=en) to Google.com, quite a nice way to really show UserJs's possibilities

imagepreloader http://userjs.org/scripts/browser/enhancements/image-preloader
Loads the images in a map for quickviewing, see it as a sort of prefetcher

lastmeasure http://userjs.org/scripts/general/enhancements/block-last-measure
Blocks certain sites that you DO not want to see. Must have for everyone that visits the ''less organized'' IRC channels.

You can find loads more scripts on Opera's dedicated website : Userjs.org or try some greasemonkey scripts : greasemonkey.mozdev.org