I'm not quite certain which is my favorite yet, but one definitely made an amazing impression on me: Scroll Bandit.
This sucker single handedly won me a game against a Vetruvian player. It was rather interesting having two Autarch's Gifts in my hand once I hit six mana. I already had lethal but cast one for fun anyhow.
Also, I second Flamewreath. It's so fun throwing it around the board and devastating your enemies. Bonus points if you cast Saberspine Seal on it.