It's just been announced on the Ubuntu mailing list that the next version of the Ubuntu OS will be codenamed the Intrepid Ibex. From the mail:
During the 8.10 cycle we will be venturing into interesting new territory, and we'll need the rugged adventurousness of a mountain goat to navigate tricky terrain.
I love the Ubuntu codenames, all based on animals. I also really like the version numbering. Incase you didn't know the version numbers are based on the year and month of release. So 8.10 is planned for release in October 2008. Ubuntu 6.06 was released in June 2006, etc.
I switched to using Ubuntu from Gentoo Linux in mid-2005. The version then was 5.04, codename Hoary Hedgehog. Since then we've seen Breezy Badger, Dapper Drake, Edgy Eft (a baby newt apparently!), Feisty Fawn, Gutsy Gibbon, and Hardy Heron (currently in Beta).
With the exception of the first few codenames the codenames go up the alphabet, meaning the next one will start with J. The Ubuntu wiki has a codename page which already has some suggestions including the Jabbering Jackal, Jovial Jackrabbit, and my favourite, the Jiggly Jellyfish.