The best animated series on television. The Legend of Korra is the sequel series to Avatar: The Last Airbender. I've always thought the mythology of the series would make an excellent setting for fantasy RPG. The Legend of Korra is currently in its Season 3, or "Book 3". All episodes of the current season are available online at the official Nickelodeon website. Links are below:
Episode 1: A Breath of Fresh Air
Episode 2: Rebirth
Episode 3: The Earth Queen
Episode 4: In Harm’s Way
Episode 5: The Metal Clan
Episode 6: Old Wounds
Episode 7: Original Airbenders
Episode 8: The Terror Within
Episode 9: The Stakeout
Episode 10: Long Live the Queen
Episode 11: The Ultimatum