Discord is Chaotic Neutral, leaning slightly toward Chaotic Good, formerly leaning toward Chaotic Evil (Fluttershy showing him that, yes, Friendship Is Magic, which is what caused the shift from CE to CN/CG).
Celestia is Lawful Good, leaning slightly toward Neutral Good (she trusts her gut and instinct more than Luna).
Luna is Lawful Good, leaning slightly toward Lawful Neutral (she came from a more formal, restrictive time period, and still needs to learn to trust other ponies and herself.)
Chaotic Neutral at best. But at least Celestia can go to the royal summit with the information that she has the God of Chaos on her side and that the Elements of Harmony are in the possession of their users. Changeling invasion? We just added 2 WMD's and they're ready to go at any time.