Its widly held that the Yondaime is Naruto's father. Plus I think its rather obvious. Blond hair, blue eyes.
Check out this manga pic and see how much they look alike:
Also its said that only Jiraiya and the 3rd Hokage know that Naruto is the 4th's son. No idea about the mother though. We can however speculate she died in child birth seeing as she isn't around.
Tsunade can't be his mom for two reasons: She was never married and she's 50 something years old.
After the showdown between the three of them (Jiraiya, Orochimaru and Tsunade) Tsunade looses all her strenght and converts back to her old looking self, though you don't actually see he face.
As I see all of what I just stated has been stated before me I think we've gotten to the key facts.
I think the more you watch and read Naruto you'll find very obvious facts.
Also consider this:
If the 4th isn't Naruto's Dad and isn't related to him at all, then why haven't we seen any other villager with blond hair that even comes close to looking like Naruto's?
