How many legacy of kain games are there?

There are currently five: -

Blood Omen: Legacy of Kain (1996)

Legacy of Kain: Soul Reaver (1999)

Soul Reaver 2 (2001)

Blood Omen 2 (2002)

Legacy of Kain: Defiance (2003)

A sixth game - Legacy of Kain: The Dark Prophecy - was cancelled in 2004 and (as of 2012) there has been no official Word on any series continuation, besides a few insubstantial rumors.