The reference
distribution for this book, and my preferred distribution, is
Debian GNU/Linux, the Linux for
  the GNU Generation.
I originally started with Slackware
in the early 90's but migrated through Red Hat and then quickly on to Debian in 1995.  Red Hat is a
good distribution and is quite popular but has limitations which,
admittedly, are being addressed.  However, Debian fundamentally
conforms to the open and distributed development model making it a
very open distribution where even you can make a change to it if you
so desired.  Debian is the basis of a number of commercial
distributions and it also powers quite a few web sites including
Linux.com.
Distributions based on Debian GNU/Linux are listed at
http://www.debian.org/misc/children-distros and include:
- GNUstep
 
- GNUstep is a LiveCD that contains a lot of software
  for GNUstep, a free implementation of the OPENSTEP framework (which
  was also the base of Cocoa in Mac OS X). Display Postscript is one
  of its powerful features. It includes an excellent application
  called Gorm for RAD (Apple Software Design Guidelines). It is
  available from http://www.linuks.mine.nu/gnustep/
 
- Knoppix
 
- The Knoppix LiveCD distribution is based on Debian and
  allows one to run Debian without installing it! Just boot from the
  CD-ROM and Debian will run from there.  If you decide to then
  install Debian, you can do so from the Knoppix CD-ROM. Knoppix works
  on most but not all hardware, trying its best to automatically
  identify hardware and set things up appropriately. See
  http://www.knopper.net/knoppix/index-en.html.
 
- Libranet
 
- Linux by Libranet packages commonly used applications
  onto an easy to install CD and includes, for example, Gnome. See
  http://www.libranet.com.
 
- Linex
 
- A Debian-based distribution being developed by the
  regional government of Extremadura (Spain) with the goal of
  migrating all the computer systems, from government offices, to
  businesses to schools into Linux.
 
- UserLinux
 
- Based on Debian GNU/Linux, UserLinux provides
  businesses with freely available, high quality Linux operating
  systems accompanied by certifications, service, and support options
  intended to encourage productivity and security while reducing
  overall costs. The project is led by long-time open source advocate
  Bruce Perens. See http://www.userlinux.com.
 
- Morphix
 
- Morphix is a modular LiveCD derived from Knoppix, with
  install images for Games, Gnome, KDE, and LightGUI. It is available
  from http://www.morphix.org.
 
- TuxTops
 
- This distributor of laptops pre-installs Debian
  GNU/Linux on their laptops. See http://www.tuxtops.com/.
 
You may also be interested in other distributions including
TimeSys for embedded real time GNU/Linux
(http://timesys.com/). See Section 4.1.1 for an
example using a LiveCD.