Good question, and such a question deserves a well considered answer. Unfortunately I'm limited for time(on lunch) but I will grant you a temporary answer until I get home later tonight.

There are many other Gospels, you are correct. You can find a list when you google Nag Hammadi. These are all Gnostic gospels, written by Gnostics. When I finish my dissertation on the Gnostics, I will have a section about just such a subject, but mainly these Gospels (and even some of the four we have in the canon) were allegorical messages about the Gnosis, and ways to achieve it through the revealer, who the Gnostics (who were the early Christians) considered to be a spiritual (Not historical) Jesus Christ.

When the anti-gnostics rose, early church fathers who in the third and fourth century destroyed the beliefs of the Gnostics by aquiring and adapting some of their teachings to a false historical concept of Jesus, and attracted quite a few more followers. When this subject matter was put up to a vote in the Vatican by bishops, the anti-gnostics won out, and the subsequent gospels were burried.

Only to be dug up later in nag Hammadi, Egypt in 1945.

Hope that helps for now.