Dr. Richard Boyan the self appointed Councilor For Earth claims 1,483 different ET races visiting earth.

http://www.drboylan.com/etraces.html

According to Clifford Stone there was 57 confirmed alien species in 1989. This video is taken from the Disclosure project's press conference in 2001:



My research has indicated a range of types:

1 - walk ins where an alien inhabits a human body and mind
2 - reincarnated aliens
3 - shapeshifter aliens that take on human form
4 - aliens that take on human form like in the V series, by cloning or other genetic means.
5 - aliens that are descended from the alien races of ancient times.
6 - aliens through a hybridization program that are really part alien, part human.

How many have you met?