How about I post them both? I find things more easily with ISBN, and some of the titles are a bit long....
Basic Connections: Making your Japanese Flow
ISBN: 4-7700-1968-8
(this is a basic book that helps sort out some of the stuff taught in the basic courses, and introduces some specific intermidiate things)
Japanese Core Words and Phrases: Things You Can't Find in a Dictionary
ISBN: 4-7700-2774-5
(this is by the same author, and kind of builds on the first, teaching a lot of ko-so-a-do phrases, and then reviewing a number of intermediate grammar concepts that show up most often on JLPT 2)
Making Sense of Japanese: What the Textbooks Don't Tell You
ISBN: 4-7700-2310-3
(this is geared more for elementary grammar, but he has the best explaination I've ever seen on the concept of wa vs. ga, and has some interesting and funny essays about other tricky basic grammar things)
Beyond Polite Japanese: A Dictionary of Japanese Slang and Colloquialisms
ISBN: 4-7700-1539-9
(this, as the name says, is a slang dictionary, and while it may not be immediately useful on a test like JLPT, I've found it indispensable for understanding anime and drama, as well as much anything that uses colloquial speech)
All About Particles
ISBN: 0-87011-954-0
(a pretty basic particle dictionary, but it does cover some advanced usages for particles that I've found came in handy; it's really good for reviewing all the possible meanings for what you already know too)
I hope these help. I would like to get a few other of the Power Japanese books that cover more select topics, but just like you, I have to figure out where to put the money before I spend it.