I’ve mentioned SourceMaking in the past for the site’s clear, concise descriptions of design patterns. As well as sections on refactoring and antipatterns, there is now a fantastic UML reference. Given how many horrific tutorials and examples I attempted to follow when I was first looking at UML, this is great news and I’d encourage you to take a look.
As with other content on the site, a premium course with ebooks and videos is also available – if you’ve paid for this, please let me know if it was worth checking out.