11. Jojen and Meera Reed
The Reed siblings are actually introduced in
A Clash of Kings, which is of course second book. Their father is a bannerman to the Starks and his children go to Winterfell to renew their pledge. The Reeds are there for almost everything that happens to Bran in season 2 including when Theon took over Winterfell. Meera Reed protects the children while Jojen Reed helps Bran with his visions. How they're going to be introduced in season 3 is still a mystery, but these two characters are pivotal in Bran's story and give some much needed spice and sense of adventure as well.
10. The Whereabouts of Sandor Clegane (a.k.a. The Hound)
During the Battle of the Blackwater, Clegane fled King's Landing and offered to take Sansa with him. Although she denied him, his story is definitely not over. He doesn't get POV chapters though, so he reappears in another character's storyline and is actually a welcome and frightening addition. The interactions between this POV character and Clegane are "different" and are definitely worth the wait.