WordTwit is a plugin that utilizes the Twitter API to automatically push a published post to your Twitter account as a tweet, using the blog domain as a short URL.
Twitter Tools This plugin creates an integration between your WordPress blog and your Twitter account. Pull your tweets into your blog and create new tweets on blog posts and from within WordPress.
TwitThis is an easy way for people to send Twitter messages about your blog post or website. When visitors to your website click on the TwitThis button or link, it takes the URL of the webpage and creates a shorter URL using TinyURL. Then visitors can sen