This is an old post from 2010. As such, it might not be relevant anymore.
yUML is an online tool for creating and publishing simple UML diagrams. It’s makes it really easy for you to: Embed UML diagrams in blogs, emails and wikis, Post UML diagrams in forums and blog comments, Use directly within your web based bug tracking tool and Copy and paste UML diagrams into MS Word documents and Powerpoint presentations.