The average user may not care too much about his login settings, but graphical environment is all the nicer if you know that nobody else has your particular desktop view. Every graphical environment has its particular ways of installing and configuring, but they all have on-line helppages. We'll list some of the most popular:
Gnome: Completely free (like in free beer) and easy-to-use desktop environment for the user, powerfull application framework for developers.
KDE: K Desktop Environment: KDE promotes ease of use, contemporary functionality and outstanding graphical design.
CDE (on proprietary systems): Common Desktop Environment
See Appendix 2 for a booklist on configuring your X server.