The IAU today has named the dwarf planet 2003 UB313 the official name is Eris, after the goddess of discord. I'm pleased to see the nickname Xena, which several astronomers and the press have been calling it, didn't stick.
Its moon has also now been named, previously dubbed Gabrielle, is now named Dysnomia, after the goddess of lawlessness (Lucy Lawless played Xena! *freaky music*).
Here's an image of Eris from the Hubble Space Telescope:
The announcement also hints at two new objects being given dwarf planet status, which would bring the number to five. Charon and Seyda (2003 VB12) maybe?