The official Twitter bookmarklet, available at dev.twitter.com, lets you share web pages to your Twitter feed with a click. You can select some text on any web page and hit the “Share on Twitter” bookmarklet to send that snippet to Twitter. If the snippet exceeds Twitter’s limit of 140 characters, you can trim a few words manually.
There’s also a new Twitter bookmarklet in town called Emph.it that works just like its official cousin but with one useful enhancement. As you are selecting text on a web page, the emph.it Twitter bookmarklet will display the exact character count of your tweet (see GIF animation) and thus you could save yourself from trimming characters later manually.
Also see: Tall Tweets
While we are on the topic of Twitter bookmarklets, you should also check out Save Publishing. When you click the Save Publishing bookmarklet, it will automatically highlight all the tweetable sentences on the current pages that fit within the 140 character limit.
I have also installed the TBuzz bookmarklet for Twitter from Arc90, the same team that developed Readability and Readlists. The TBuzz bookmarklet will not only help you posts links to Twitter but it will also show you existing tweets that have recently posted to Twitter around that web page. This is handy information in case you wish to know what others are saying about that page.