Ubuntu 13.04 has been released, here's how you can download it. Note that you can also download other spins of Ubuntu, including Kubuntu and Lubuntu, among others.
http://releases.ubuntu.com/13.04/ (Ubuntu Desktop and Server)
http://cloud-images.ubuntu.com/releases/13.04/release/ (Ubuntu Cloud Server)
http://cdimage.ubuntu.com/netboot/13.04/ (Ubuntu Netboot)
http://cdimage.ubuntu.com/edubuntu/releases/13.04/release/ (Edubuntu DVD)
http://cdimage.ubuntu.com/ubuntustudio/releases/13.04/release/ (Ubuntu Studio)