Ubuntu 9.04 has been released this morning along with the 9.04 "Jaunty Jackalope" updates to Kubuntu, Xubuntu, Edubuntu, Mythbuntu, and Ubuntu Studio. With Ubuntu 9.04 there also remain the server and Netbook Remix spins.
There are download links for the *buntu 9.04 releases within the Canonical release announcement
. Ubuntu 9.04 features EXT4 installation support, a new notification system, GNOME 2.26, a slightly updated kernel, and many other changes. More details on this new release by Mark Shuttleworth's company can be found in a Ubuntu 9.04 search