This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
There are many diagramming software which will help to draw class diagram, however I use Visio 2010 to draw UML and other diagram. Visio 2010 can create class diagram by reverse engineering. I will recommend you to try it out with the free trial version available for evaluation purpose.