Super Grub Disk 0.9795 features ext4 support.
Ext4 support means that it will work with Ubuntu 9.04.
Enjoy it!
adrian15
P.S.: Unfortunately I could not build Super Grub Disk floppies that booted without problems. I will try to build them but I do not promise anything. I haven't still understood what exactly you need to build a floppy image that boots.