How many sharingans are there in naruto?

There are currently 4 known holders of the sharingan. It seems all 4 possess the Mangekyou Sharingan.

Uchiha Sasuke - He has shown the abilities of his brothers Mangekyou Sharingan while also displaying greater control over it's powers.

Hatake Kakashi - Has shown the ability to create a dimensional hole and suck/rip anything in his focus out of his reality.

Danzo - Has shown the ability to control others. To what extent it's not yet clear.

Uchiha Madara - Has shown the ability to phase out of corporeality, teleportation and the ability to send others to a personal dimension.