Fusion Cydia tweak allows you to post to multiple social networks at once. It integrates Facebook, MySpace and Foursquare into default Twitter sheet.
Check the video review after the break
It also includes quick composing feature, you can assign an activation method in Activator to launch the tweet sheet. Fusion also allows you to use Siri to post to any of the social networks that are supported.
Fusion jailbreak tweak is available in Cydia under the BigBoss Repo for $2.