Here is the DMG's list:
A total of 80 individual items. Where a character's studied artifacts are concerned, I would treat each and every separate form of an item as a completely unique artifact.
Plus the following list that I have had appear in my world at some point (some of which are obvious in an Earth-based world):
Ark of the Covenant
Cup of the Ptolomies
Nail of the Left Hand Further information here.
Taurlobolic Altar of Lugdenum
Theotokos of Kazan
Venus of Dolni Vestonice
Venus of Willendorf
Add to this the list from the Deities & Demigods:
Finally, if more are wished for, I have this list on wikipedia to plunder from (though I've already included a few). That list adds (approximately) 312 additional items, for a total of 424 total artifacts.