WordPress.com introduces "Twitter Blackbird Pie," that displays tweets as rich full content rather than as just simple URLs or images. With Blackbird Pie Twitter, hashtags link to search pages and usernames link to twitter profiles. An individual tweet, or pie, includes all the details, design, and information that a single tweet page would include. Twitter Blackbird Pie will work for posts and comments throughout WordPress.com.
To embed a tweet in your blog, just visit the tweet on Twitter.com, copy the URL from the address bar, and paste it into your post on a line by itself. WordPress.com will do the rest and your link will be converted into a full tweet once pull the relevant data (there may be a short delay).
Self-hosted WordPress blogs, can use Twitter Blackbird Pie plugin.