Social Syndication is* a suite of modules that allow you to automatically post your Drupal content to Twitter and will add Facebook and Google Plus in the near future.
REQUIREMENTS
Oauth module: http://drupal.org/project/oauth
You will need to create an 'app' for Oauth authorization at http://dev.twitter.com
OPTIONAL HELPER MODULES
Shorten Module: http://drupal.org/project/shorten
INSTALLATION
Download the Social Syndication module and place the unzipped folder into /sites/all/modules/ or /sites/all/modules/contrib
Enable Social Syndication and Twitter syndication
Enable permissions at /admin/people/permissions
Post Content to Social Media
Send Content to Twitter
CONFIGURATION
Create a Twitter app at http://dev.twitter.com and enter the required Oauth tokens at admin/config/services/social_syndication/twitter
If you want to connect a Bitly account, you may enter your account name and API key at admin/config/services/social_syndication/bitly
If you want to be able to include the Twitter handle of the currently logged-in user with a Token, you can add their Twitter handle in the User edit form (admin/people).
Configure posting options at admin/config/services/social_syndication
Twitter username: the account which content to which content will be posted