God

God created the heavens and the earth. He has yet to make an appearance in this show. 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 to find him and "hold him accountable" for his actions. He is nowhere in Heaven but somewhere on earth though Dean sarcastically remarked that God was either in Mexico, dead, or drinking in Hawaii.

It is revealed in the episode Good God Y'all that aside from Michael God is the only one strong enough to defeat Lucifer and end the apocalypse and acording to Castiel it was he who ressurected the angel and saved the boys from Lucifer's rising. Also the amulet that Dean wears is revealed to be a sort of God tracking device and will glow and become hot in God's presence.

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 to demon blood) and he guesses that both he and Zachariah know the answer. At this, a shocked Zachariah mumbles that it's not possible and Castiel tells him it scares him. Castiel then politely but bluntly tells him to put the boys back together and back off, to which the higher ranked but heavily intimidated angel complies. This suggests that even though God isn't actually present he is very much aware of the current situation and is able to monitor things even when he is not present.

In Free to be you and me Raphael; one of the few archangels who has actually seen God says that God is dead and claims that it was Lucifer who revived Castiel so he could corrupt him to their side. However after Dean continues to slander the angels and God, Raphael reveals that God actually just up and left heaven without word or instruction on how to look after things. Why God left is unknown but considering that Dean was saved as well as Sam who has been revealed to be the Devil's true host when it would have been more logical for Lucifer to kill Michael's vessel seems to suggest and confirm it was God who saved the boys and raised Castiel and he is out there in some form or another.

Lucifer claims that God banished him for simply loving him too much and for refusing to bow to human who the angel so has inferior and flawed. God had however made man with free will, a gift the angels lack and knew that even though God knew man could do evil they also had the potential for great good, so long has they had proper guidance. He tried to explain this to Lucifer but the jealous livid angel refused to listen. God eventually saw there was no help for Lucifer especially after he created the first demon (Lilith) and was forced to banish him to Hell. Dean even guessed that God had no doubt that Lucifer was beyond help.

Known angels of heaven
Castiel 

Anna Milton (A fallen angel)

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

Zachariah (Zachariah was Castiel's superior.)

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

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

The Archangel Gabriel 

The Archangel 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 may be the only one who knows where God is)

The Archangel Uriel (An archangel who takes part in the apocalypse)

Family
Everything living (God's creation)

The Angels of Heaven (servants)

Jesus Christ (son)

The Archangel Lucifer (God's first angel)

The Archangel Michael (God's second angel)

The seven angels of God's wrath (One of god's greatest weapons in the war against hell)

Humans (children)

Powers
Voice of Authority - God's voice alone created the heavens and the earth. His voice has authority over all of creation.

Overwhelming appearance - God's full appearance (his face) would kill any human instantly. Moses saw god's appearance from the back; so he didn't die. Special archangels can withstand god's true visage. It has been stated that only four angels have seen god; Lucifer, Michael, Raphael and Gabriel.

Omnipotent - God is all powerful in ways that have no logic or explanations. Nothing in creation can physically hurt god.

Omnipresent - God is present everywhere; nothing can hide from god.

Omniscient - God possess infinite knowledge of the universe.

Immortality - God is eternal and everlasting. God is immortal therefore he can't die.

The trinity
God 

Jesus Christ 

Holy Spirit 

Appearances
Sympathy for the Devil - God interfered for a brief moment; he teleported the Winchesters to a safe location (away from Lucifer). God teleported them on to a plane; this was before the chapel was destroyed by Lucifer's presence.

Names
Savior 

Lord