By default, ubuntu-server 8.04 does not come with any graphic desktop environment or GUI. Which is natural, because it is server. However, sometimes it would be useful to have some GUI. It is not a problem to install it. Admins have quite a few options for GUIs. Here I will show only few of them.
Method
The following examples were performed using ubuntu-server 8.04.2 installed as a guest os in VirtualBox 2.1.2. The screenshot of a system was performed just after the fresh install of ubuntu. After installation of each desktop the system was reverted to current snapshot. Therefore, in each example, only one GUI was present in the system. For each example /etc/apt/source.list was not modified. All desktops are available in default ubuntu repositories.
To start any of the following GUIs after they have been installed, the following command can be used:
To start any of the following GUIs after they have been installed, the following command can be used:
startxubuntu-desktop
sudo aptitude install ubuntu-desktopThe command will take 560MB of space. This amount includes about 37MB for xorg. It installs full ubuntu/gnome desktop with every software normally available in ubuntu-desktop (OpenOffice, Firefox, etc...). It takes quite a long time to install. The main disadvantage of this, is that it de facto converts ubuntu-server into ubuntu-desktop. This has not much sense, since we want ubuntu-server and not ubuntu-desktop. However, such an option exists, and in some cases it may be useful.
Instead of gnome base ubuntu-desktop, in a similar way, user can install kubuntu-desktop or xubuntu-desktop.gnome-core
sudo aptitude install xorg gnome-coreThe command will download about 160MB. It also takes a bit of time to install. As the name suggests it installs only basic gnome functionality.
xfce4
sudo aptitude install xorg xfce4The command will download about 80MB. Again, as the name suggest, it installs xfce4 desktop environment. Installation time is not so terrible. 
enlightenment
sudo aptitude install xorg enlightenmentThis will download about 50MB.
fluxbox
sudo aptitude install xorg fluxboxThe command will download about 39MB. It must be rememberd that xorg is about 37MB! Hance, fluxbox is about 2MB! Most of the installation time is used for installing xorg. 
twm
sudo aptitude install xorg twmIt will download about 38MB. It must be remembered that xorg is about 37MB, therefore twm is about 1MB!
ctwm
sudo aptitude install ctwmThe command will download about 38MB. This is slightly improved version of twm. Specifically it adds virtual desktops. However, for me there was some problem in that I could not navigate through the menu.
vtwm
sudo aptitude install vtwmThe command will download about 38MB. Again, this is slightly improved version of twm. Specifically it expands desktop. 
Conclusions
There are many desktops that can be installed in ubuntu-server. As far as I am concerned, for me the smaller desktop the better. This is because, they do not consume lots of server resources, their installation is fast, and they are perfect for using with vncserver. Therefore, I would recommend fluxbox, twm, ctwm or vtwm.
