Emphit is a neat little browser tool that allows you to highlight any text in a webpage and tweet it. A count shows the characters you highlight as well.
As long as the text is not inside an image file it worked quite well in tests. You drag their button to your toolbar, select any text and tweet away including a link to the page you are on.
As the promote for the tool, this makes tweeting something from a webpage faster than most people couple type it out and link it.