4. Wylla
The name of Jon Snows mother, or at least who is said to be her, is actually confirmed in the books. In A Game Of Thrones, Ned has a conversation with Robert Baratheon in which they discuss the topic of Jons mother:
You told me once. Was it Merryl? You know the one I mean, your bastards mother? Her name was Wylla, Ned replied with cool courtesy, and I would sooner not speak of her.
There, in the very first book (and the conversation is repeated in just the second episode of the show), its stated that a woman named Wylla is the mother of Jon Snow, and the person who somehow managed to make Eddard Stark beseech his famous honour. So who is Wylla? We learn more about her in A Storm Of Swords, and receive further confirmation that she is indeed the one who gave birth to Jon. In a conversation with Arya, Edric Dayne - Lord of Starfall - states that he and Jon are milk brothers as the latters mother was his wetnurse. He gives her name as Wylla. In the TV show, however, we dont see this conversation take place. So, two separate sources in the book seemingly confirm that Wylla is the mother of Jon Snow, and thats that right? Er, not exactly