Funny, just had the Planescape boxed set open...
Doomguard - Everything dies and breaks down, these guys are here to help it along
Mercykillers - Break the law, and you deserve to die. These guys enforce that.
Sensates - New sensations help to refine what is pleasurable or not. Pain or ecstasy, you can't know the heights of one without having experienced the depths of the other.
Xaocists - All is chaos - don't try to make sense of the universe.
The Athar - The gods are liars who are trying to keep power for themselves. You have the ability to rise above them and seize the power for yourself.
Godsmen (Believers of the Source) - Live the "good" life and keep getting reborn 'til you get it right and turn into a god/ascended being.
Bleak Cabal - "End the Universe, I want to get off"; life is a joke and you're doing folks a favor by showing everyone how futile living is.
The Dustmen - If everyone would just up and die and go to their rightful plane as petitioners, this universe would be a whole lot better off
The Fated - Your destiny is already planned out, so stop dawdling and start seizing your destiny now
Guvners (Fraterity of Order) - Without law and order, the universe would fall apart. Their job is to make sure things don't collapse
Indeps (Free League) - You are your own master, don't let anyone else tell you what to do
Hardheads (The Harmonium) - Big brother is watching you; We know what is good for you - we are your mother and your father ...
Anarchists (Revolutionary League) - Throw down the order of the multiverse; it's too corrupt to continue to exist
Signers (The Sign of One) - Only you exist; everyone and everything else around you is a dream in your own mind
Ciphers (Transcendent Order) - Thought is the ruination of the multiverse; Only by action without thought or qualm can you purify mind and body