The first manga that leaps to mind is the Rosario + Vampire Manga. The anime is fun to wacth, but the manga has much more action and a more mature vibe to it (just a little). It's not the best manga out there but it's enjoyable. It has 10 Volumes (english version), and Rosario + Vampire Season II is currently on it's 2nd Volume (english version). Pick it up if you have the time.