Gimp

GIMP is a great free software for photo retouching, image composition and image authoring. It works on many operating systems, in many languages.

GIMP Totorial
URL: http://gimp.org/tutorials/
These are the tutorials at the gimp.org site. They are arranged into categories including Beginner, Intermediate, Expert, Photo Editing, Web, and Script Authoring.
Grokking the GIMP
URL: http://gimp-savvy.com/BOOK/index.html
This is an entire free GIMP book that is available to read online or download in html format.
GIMP User Group
URL: http://gug.sunsite.dk/?page=tutorials
The GUG contains tutorials for various versions of the GIMP.
Basic GIMP Tutorial
URL: http://www.ufocomes.de/files/basegien.html
Draw a stickman in GIMP. This tutorial is also availabe in German (Deutsch).
A Tutorial for Perl Gimp Users
URL: http://imagic.weizmann.ac.il/~dov/gimp/perl-tut.html
Perl as a language is probably more familiar to the web-literate users, as it is the major language for writing CGI scripts. Now, Gimp scripts may also be written with Perl. This tutorial will describe how to write such plug-ins and scripts for Gimp.
Beginners Guide to The GIMP
URL: http://bachue.com/alejo/gimptutorial.html
This guide covers the 1.3 version of The GIMP.
Gimp Tutorials
URL: http://tigert.gimp.org/gimp/
Some GIMP tutorials and resources.
Getting Started with The GIMP: an informal tutorial
URL: http://www.gilesorr.com/papers/gimp-tutorial/gimp.html
This tutorial is highly informal, and is a walk-through of some fairly basic things that can be done with the GIMP
Gimp-Tutorial
URL: http://www.linuxnetmag.com/en/issue4/m4gimp1.html
A two-part gimp tutorial that uses an animated banner as an example.
The Gimp Tutorials - Phillip Riley's Homapage
URL: http://www.geocities.com/phillipriley/comptutgimp.html
Buttons and backgrounds tutorials
How to Use GIMP for Photo and Image Editing
URL: http://www.mozillaquest.com/OpenSource04/Gimp-Photo-Edit-Tutorial-01_Story01.html
A tutorial from LinuxNetMag that focuses on the basics of using GIMP's cropping, scaling, brightness adjustment, and contrast adjustment tools. You will learn how to use these tools by editing a digital photograph.
GIMPguru.org
URL: http://www.gimpguru.org/
GIMPguru.org is a resource for those using the GNU Image Manipulation Program (GIMP) to edit photographs. The site includes tutorials and a forum.
Photo Touch Up and Enhancement in the GIMP
URL: http://www.geocities.com/SiliconValley/Haven/5179/
The purpose of this tutorial is to explain how the GIMP can be used to touch up and enhance your photos.
The RRU Gimp Tutorial
URL: http://www.rru.com/~meo/gimp/Tutorial/
N/A
GIMP Tutorial
URL: http://members.cox.net/wcommerc/the_gimp/the_gimp.shtml
A pretty short tutorial series with some basics about photo editing, text effects and drawing lines.
GIMP User FAQ
URL: http://www.rru.com/~meo/gimp/faq-user.html
Answers to about a hundred commonly asked questions about the GIMP.