The official Ubuntu book

Ch. 1. Introducing Ubuntu

Ch. 2. Installing Ubuntu

Ch. 3. Using Ubuntu on the Desktop

Ch. 4. Advanced Usage and Managing Ubuntu

Ch. 5. Ubuntu Server

Ch. 6. Support and Typical Problems

Ch. 7. Ubuntu Community

Ch. 8. Using Kubuntu

Ch. 9. Using Edubuntu

Ch. 10. Ubuntu-Related Projects

Ch. 11. Introducing the Ubuntu Forums

Appendix A. Welcome to the Command Line

Appendix B. Ubuntu Equivalents to Windows Programs.