I successfully ported XFCE Ubuntu 9.04 on to BB
--seed metacity,gdm should work... Otherwise "ubuntu-desktop", just
make sure to have a good gig of swap..
you can look up packages at http://packages.ubuntu.com/
for gnome it says
"This package depends on the standard distribution of the GNOME
desktop environment, plus a complete range of plugins and other
applications integrating with GNOME and Debian, providing the best
possible environment to date. "
so that will probably get you most of a working gnome,
http://packages.ubuntu.com/jaunty/ubuntu-desktop gives you quite a lot