KDE has many excellent system configuration utilities. The same applies to Gnome. There's also the "gnome-system-tools" package, which you can install to configure certain system properties via a GUI frontend even if you're using some light-weight wm instead of KDE or Gnome.
Also, Debian uses DebConf to configure many important packages. You can install gkdebconf and libgnome2-perl packages to get a GUI frontend for "dpkg-reconfigure" that can be used to (re)configure the packages that DebConf controls. (After installing these packages, run "gksu gkdebconf" from xterm to invoke gkdebconf.)
The APT (Advanced Packaging Tool) related utilities (dpkg, apt-get, apt-cache, aptitude) are VERY useful in Debian. You can get a quick introduction to these utilities by typing the desired command in command line followed by " --help".
For instance, you can check out all the packages that are installed in your system by typing "dpkg -l | more". To see where APT has placed the different files from the package "foo", you can do "dpkg -L foo". And to find all the available Debian packages that have something to do with printers, you can do "apt-cache search printer". Etc, etc...
The Debian Wiki page here at linuxquestions.org gives you a good overview on what Debian has to offer. Utilities like modconf, update-rc.d, and update-alternatives are briefly introduced. Once you get started with these utilities, you may want to check out their man pages. (I really mean it -- once you get familiar with some command, you'll do wisely if you Read The Friendly Manpage.)
http://wiki.linuxquestions.org/wiki/Debian
