God

God created the heavens and the earth. He has yet to make an appearance in this show. However he will be making a appearance in the latter part of the fifth season. At the start of the fifth season it is confirmed that God does exist but nobody knows where he is meaning he is technically "missing". Lucifer doesn't even know where God is and made it clear that he wishes the find him and "hold him accountable" for his actions.

Even though nobody knows where he is it is suspected that he is helping the Winchesters and was the one who brought Castiel back. This is supported by the fact that when Castiel rescued the boys from Zachariah the shocked superior asked how Castiel was still alive. Castiel responds he doesn't know and more to the point asks how the boys escaped being blasted to bits in the church; because it wasn't the angels who zapped them on to the plane(and cured Sam's addiction) and he guesses that both he and Zachariah know the answer. At this a shocked Zachariah mumbles it's not possible and Castiel tells him it scares him and the he politely tell him to put the boys back together and back off which the higher ranked but heavily intimidated as of now angel does. This suggests that even though got isn't actually present he is very much aware of the current situation.

Known servants
Castiel 

Anna Milton (A fallen angel)

Uriel (Uriel betrayed God when he started murdering the angels)

Zachariah (Zachariah was Castiel's superior. He too betrayed God)

Lucifer (At one point Lucifer was an angel, but he disobeyed God and was sent to Hell)

Michael (God's Lieutenant and the one who personally "kicked" Lucifer out of Heaven during the last war and possible the only thing that beat him again)

Raphael (Will appear in season 5, not much is known of him at the moment except he supposedly went AWOL after the last war and maybe the only one who knows where God is)

God has thousand's of angels under his command 

Family
Everything living (God's creation)

Angels and humans (children)

Jesus (son)

Powers
Omnipotent

Omnipresent 

Omniscient

God is able to do absolutely anything, even the logically impossible.

Immortality 

Godlike strength

Godlike endurance and stamina 

Godlike speed