The first DLC for Brink is expected to be out early this July.  The Agents of Change pack will have two new stages, a new ability for each class, two new weapon attachments, and two new outfits so you can play dress up with your friends.  You can see them all detailed here.  The new abilities may look familiar to anyone who hit the level cap.  They pop up when you hit level 20, then disappear.  At least they used to, this may have been patched away by now.  I'll finally get to use those Napalm Grenades I unlocked back in May!