Bookmarklets are small Javascript applications stored in the URL of the link that, if dragged to your bookmark toolbar, can be used to do cool things when you click them. Here are a couple:
  1. Add an image to your Gmail message
  2. Add HTML into your Gmail message (a more general form of the above)
  3. Make all frames (and subframes) editable (click again to make them all uneditable)
  4. Get the URL of the Facebook image you're viewing
  5. Get prices for woots
Try them out! And if you like these, please Digg this post.