Heaven

Heaven is a wonderful place. God created heaven. It has been stated that only four angels have seen God. God lives in heaven with his angels. The true form of an angel may be overwhelming to most humans. Michael, Raphael, Gabriel and Lucifer have all seen God's face. God is currently not in heaven; his location is currently unknown but it is thought possible that Raphael knows where God is, however he denies this and claims "god is dead", as this is the only possible explanation for gods 'abandonment'. Even though God isn't present it is possible he can still monitor and watch over the earth. Even in heaven angels can speak with their vessels.

Known angels
Castiel 

Anna Milton (A fallen angel)

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

Zachariah (Zachariah was Castiel's superior.)

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 possibly the only thing that beat him again, current ruler of heaven 'the viceroy of heaven')

Raphael ( appears 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, he is chuck's archangel guardian)

Gabriel (This angel has yet to make an appearance in this show, is an archangel)

The Angels of Heaven

Current inhabitants
Michael (ruler of heaven, chief Archangel)

Gabriel 

Anna Milton 

The Angels of Heaven 

Leaders of Heaven
Michael (Current leader)

God (Rightful King of heaven)

Heirarchy of angels
Archangels ( rulers of heaven, most powerfull angels, command even the seraphim)

Seraph (Seraph are the highest 'species'/ order of the heirarchy of angels, some archangels are also seraphs such as Michael and Lucifer )

Cherubm (Cherubm are the second highest order)

Thrones (Thrones are the third highest order)

Angels 

Known archangels and high ranking angels
Michael (Defeated Lucifer, ruler of heaven, chief of the archangels, prince of the seraphim)

Gabriel (This angel has yet to make an appearance in this show)

Raphael (This Angel has yet to make an appearance)

Lucifer (At one point Lucifer was an archangel, once one of, if not the most powerfull, high-ranking and beautifull angels )

Zachariah (Zachariah is not an archangel but he is more powerful than a normal angel)

Higher Up angels (Higher up angels have the ability to summon other angels back to heaven)