Somewhere I heard around 11,000. I imagine there are a lot of branches of Islam too. There were a lot of different Bhuddist sects that I saw while I was in Korea.
Out of curiosity, I did a search and came up with this link:
http://www.bringyou.to/apologetics/a120.htm
Quote: Also, according to the United Nations statistics there were over 23,000 competing and often contradictory denominations
Read through the article. Numbers vary somewhat between sources but it really boggles the mind.