A Frequency Dictionary of Mandarin Chinese
Routledge
The 5,000 commonest words in Mandarin, in order of how often they actually occur in a large corpus, each with a real example sentence. This answers the question no lookup tool can: what should I learn next. It also settles arguments — when you suspect a word you keep meeting is more important than its HSK level suggests, this is where you check. The thematic lists at the back are the most useful part and almost nobody mentions them.
What it does not do: It is a linguistics reference, not a study book: no exercises, no progression, no audio. It is also the most expensive item in this category and the corpus behind it is not recent, so internet-era vocabulary is under-represented.
Free here first: Our own character and word frequency data, free