WP.me short link (tiny URL) will help you to shorten your URL links. Infact WP.me itself i a short url for http://wordpress.com/. You can use this short url in Twitter or in other socail media website.
WP.me is similar to Tiny URL but it is different in a few ways. By default every blog and post on WordPress.com has a WP.me URL and the links are permanent. WP.me exposed in the using rel=shortlink.