Ignore the wretched cover design, with its physically painful use of letterspaced Lithos Bold. Readers Guide to Intermediate Japanese is not the cheesy self-published unedited piece of crap it appears to be. (honestly, if it hadn’t been from University of Hawai’i Press, I wouldn’t have bought it on a bet)
This is an excellent reference to written Japanese, filled with clear explanations of the things you start running into when you step outside of prepared student texts. It neatly supplements the three volumes of Makino/Tsutsui’s grammar, filling in some important gaps. It also provides some useful cross-references to similar phrases and standard forms, for the student who isn’t sure if he should be looking up chigai nai or ni chigai nai, etc.
Perhaps most immediately useful is the 19-page section listing common variations of ki ga/ni/o X and 9 pages of mi ga/ni/o X. You pick up some of this in textbooks, but it’s very nice to have it all in one place.
Sadly, as usual there is no ebook edition. Someday, you’ll be able to carry around thirty pounds of reference books on an 8-ounce reader, but not today.