Use the video demonstration on TallTweets.com to create tweets longer than 140 characters.
This tool offers two options for sending long tweets: 1.) tweet storm (breaks long tweets into 140 character chunks); and, 2.) tweet image (convert longer tweets into an image - all-in-one).
The catch: the services wants permission to post for you...as in, after you compose your long tweet using this service, the service will chunk or image the tweet, then post to your twitter account. If you do not want to allow this service access to your twitter account, don't use the service. Instead, you can write your tweet in an image editor, save as the file as a .JPG and tweet the picture yourself.