How many greek myths are still told today?

It depends how you define "famous." Furthermore, it is hard to define what makes up a full myth. Someone might say that everything pertaining to the Trojan War amounts to one myth, while someone else might say that the Trojan horse, the death of Achilles, Odysseus's journey home, etc. are all individual myths. Someone might divide Odysseus's trip into even smaller "whole" myths and decide that some are famous and some are not.