According to a message posted on the Ubuntu mailing list by Mark Shuttleworth, the leader of the Ubuntu project, the codename for the 9.04 release of Ubuntu will be 'Jaunty Jackalope'.
I guess Ubuntu fans are already used with the funny codenames each new release has, and usually there is a forum thread for name suggestions permanently back at UbuntuForums. Jaunty Jackalope will most likely be released in April 2009, the first number meaning the year (2009), while the numbers after the dot represent the month. More details on the release cyle here.
Wikipedia has an article about 'jackalope' as being an imaginary creature described by a cross between a jackrabbit and an antelope, goat or deer, often portrayed as a rabbit with antlers. Although Mark Shuttleworth talks about it as a 'Warrior Rabbit' (a comparison for Ubuntu's fight over marketshare I guess), jaunty can have the meaning of 'happy' or 'careless', hence, a Jaunty Jackalope, or a happy rabbit with antlers, or similar.
According to Mark Shuttleworth, 'Jaunty, the code name for what will most likely become Ubuntu 9.04, will be the focus of our efforts from November through to April next year.'
Let's hope for a good and (if possible) almost bug-free release.