Reference:HSK Standard Course
These are the textbooks released by Beijing Language and Culture University Press, released in cooperation with the Hanban (the organization which oversees the HSK). This series is the most authoritative HSK test prep material. Click on the book covers below for more information on each book, including the grammar points contained in each.
If you're using these textbooks, be sure to check out AllSet Learning's HSK-Mod Courses.