Debian codenames to date have been Buzz, Rex, Bo, Hamm, Slink, Potato, Woody, Sarge, Etch, Lenny, Squeeze, Wheezy, and now Jessie with the next release. The codenames are names from the Toy Story franchise. Debian 9.0 will now apparently be codenamed Zurg, an emperor toy from Toy Story 2 and Toy Story 3.
There's been talk in the Debian camp before of using the Zurg codename, but now according to Dimitri John Ledkov in this blog post, Zurg is the 9.0 codename. Update: Apparently Dimitri John Ledkov's statement was incorrect and Zurg is not (at least not yet) officially the codename for Debian 9.0.