The book, Using OpenRefine, has been a really good resource, but is there anything better?
2 Answers
The documentation page on OpenRefine website point out to the official wiki a list of tutorials and the discussion list for your project specific questions.
Like @Joe pointed out, I am not sure what are your looking for exactly. Maybe you can explain what you are tying to learn and why the book or existing documentation doesn't address your challenge.
(disclaimer I am part of the OpenRefine team)
Have a look at these three videos if you like watching tutorials.
Otherwise the list mentioned by @magdmartin is quite extensive.