As an initiative of Benjamin Humphrey, in 2009 The Ubuntu Manual sees the first light.
Now after a year of hard work, they release their second edition of a great manual of 168 pages.
Covering from Ubuntu installation to security and troubleshooting, going through hardware and other topics. This is a great guide and a must have for anyone (Individual or company) trying to start with Ubuntu. If you think you can collaborate with them, see here how to get involved with this project.
It does not matter if you are a beginner or an advanced user, download Ubuntu Manual and start or continue learning.