With the Twitter Publisher plugin you can send automated tweets out when you publish a new post. It will add Google Campaign variables to the URL using the new URL shortener Awe.sm of Bit.ly. For larger blogs, with multiple authors, you can include the author’s Twitter name in the tweet and individual author’s can send Tweets from their account at the same time the main account is sending them.

You can download the plugin on Wordpress.org, or search for Twitter Publisher in your Wordpress installation under Plugins -> Add New