Since people are wondering what the next world might be after Azteca, or the next side world, I thought I'd make a list of mentioned worlds (and where they were mentioned) from both Pirate and Wizard.
Gobblerton: home of the Gobblers; overrun by witches; possibly the "Candy World". (Wizard City)
"Candy World": home of Professor Greyrose; possibly Gobblerton. (Wizard101 Message Boards)
Empyria: home of the Sky Squids; cloud world? (Wysteria)
Mirage: Arabic themed? Persian themed? (Wysteria)
Yago: world with "star fields"; home of Helephants? (Wysteria)
Darkmoor: home of Lagooneys; Halloween themed? (Pirate101- Cool Ranch)
Polaris: French and/or Russian themed; ice world. (Zafaria)
The Brisk Land of Nodor: home of Wooly Mammoths and Frozen Fomori; Antartica world? (Avalon)
Rajah: Indian themed under English (Marleybonian) colonial rule; home of tigers. (Pirate101- Marleybone)
Of course there's the possibility of a world not even mentioned, or even a world from Pirate101 (though at the young age of Pirate101, I doubt it).