To my knowledge there are 7 kai's, they are as follows:

1. West kai, East kai, North kai, South kai
2. Grand kai
3. Supreme kai (Shin)
4. Elder Kai

1. West, East, North, South Kai - They all watch over their own section called a Quadron or a Universe. 
2. Grand kai - He watches over 4 the kai's and their quadrons.
3. Supreme kai - i think he does the same as the Grand kai except he is more experienced and knows alot more about the qaudrons and their inhabitants.
4. Elder kai - Not to much is known about him except that he was trapped inside the Z sword for 14 generations.  He was release from the sword when Gohan was testing the strength of the sword against a rock that Goku threw at him.   The Z sword shattered when Gohan hit the rock. Therefore releasing the Elder kai from his imprisonment.