So I just finished watching season 2 of Legend of Korra, and I'm certainly not done. I realize she basically did her job as Avatar and saved the world. Is there a season 3 in the making? oder a whole new series of a new Avatar?

Yes. Nickelodeon has ordered season 3 and 4.
Season 3 is called "Changes" and will deal with how Korra handles being Avatar now that there are spirits in the physical world. It will also focus Mehr on the Earth kingdom (yay! Mehr Lin Bei Fong). The 4th book will focus Mehr on the feuer nation. There hasn't been an announced released datum yet for season 3.

Season 3 is playing right now! New episodes every Friday!