2003 UB313 has been given the name Eris.
The BBC have pointed out how appropriate this is.
Everybody else on the internet is saying "Hail Eris!" "All Hail Discordia!" and "Kallisti!". If you don't know why then this slightly po-faced wikipedia page may assist you.
It also means the free solar system chart I got in Tuesday's Independent is already out of date. Welcome to the 21st Century!