Being a Mandarin Chinese teacher, I have many Chinese learning reference books on hand, but so far, Wolfe's book Chinese 24/7 is my favorite. This book covers topics such as Chinese pronunciation, grammar, common expressions and culture all in one and it's suitable for learners of all levels.
This book is extremely practical. The sentences and phrases introduced in this book are very useful but they are usually hard to find in traditional Chinese textbooks. I remember the first year when I moved to the U.S., I couldn't understand it when Americans asked me "What's up?" or "how's it going?" because sentences like these are seldom introduced in the textbooks. The only thing we have learned is "how are you?" The same goes with the Chinese textbooks. Many of them introduce "ni hao ma? (How are you?) as the Chinese way of greeting while this expression is not common in real life at all. Wolfe's book focuses on the practicality of the language that enables the readers to put the language to use immediately after studying it.
In addition, as a seasoned learner himself, Wolfe is able to foresee learners' problems and to clarify many confusing concepts your Chinese teachers do not even have answers for. For example, this book explains the subtle difference between "rou" and "hun cai". If you look up these two words in the dictionary or textbooks, you will notice that they both mean meat, but in reality, they are not exactly the same. Wolfe explained this very clearly in his book. "Hun cai" actually includes fish and seafood while "rou" doesn't. Chinese teachers, such as myself, won't naturally have an explanation for concepts like this because we simply have taken our mother tongue for granted. We just use it without thinking about it.
In summary, this Chinese reference book is practical, fun and comprehensive. I wholeheartedly recommend it!