marco_b

This plugin updates your twitter status with the latest post that you’ve made. It also has the option of including a link back to your post so people can easily click on it to view the post. 
The link provided in the tweet can be shorted via a service of your choice: tinyurl.com, is.gd, bit.ly or snurl.com
If you wan to stay up with me, you can <a href="http://twitter.com/marcobischoff" rel="nofollow ugc">follow me</a>. 
Enjoy!
<h3>Features</h3>
With this version it is possible to update more than one twitter account.
Still missing is the following: 
ow.ly as shortener service 
React on posts which are written for the future

Twittrup

Updates Twitter when you create a new blog post utilizing an shortener service of your choice.

This plugin is not for most WordPress users. It will stop WordPress from automatically updating witch is not recommended. The only reason you might need this plugin is if you have modified your WordPress core files and you want WordPress to stop overwriting them with their automatic security updates. Otherwise you should probably just let WordPress auto update.
Updated April-19th

Stop Auto Updating Dangit

This plugin simply stop WordPress from automatically updating for you.

Twittrup vs Stop Auto Updating Dangit