According to Etnologue the answer to this question is 6 809, however near the half of them is on the way to disappear totally, as many languages are spoken only by a handful of old people, or a small ethnical group.
Linguistic Society of America wrote a nice and detailed study where you can read more about this question.
http://docs.google.com/viewer?a=v&q=cache:O9TVpYVyUDEJ:www.lsadc.org/info/pdf_files/howmany.pdf+how+many+languages+are+there+in+the+world&hl=hu&gl=hu&sig=AHIEtbQWpLAQPypMW_UKqZwyIuXBzNSi5g
More about Ethnologue: http://www.ethnologue.com
pirms 14 gadiem
500