The Dictionary of Japanese Grammar Series (Basic, Intermediate, and Advanced)
In 2008, the Dictionary of Japanese Grammar series was finally completed, and it is a great aid for the JLPT, particularly if you are studying on your own. For 1kyuu prep, I highly recommend A Dictionary of Advanced Japanese Grammar, the third volume of the series; if you can, I'd purchase all three, but you don't need the first two to get a lot of use out of the third volume.
Produced over the course of two decades, the Dictionary of Japanese Grammar is the definite Japanese-English grammar dictionary series.
Although I generally recommend using Japanese to study Japanese, some of the JLPT grammar is particularly tricky and it helps to have an English explanation. In this respect, the series is fanastic.
Each grammar point is explained throughly, with 1-5 key sentences that demonstrate the use (or uses) of the pattern and the way it conjugates, followed by 5-15 example sentences (with English translations), which are followed by notes on the grammatical pattern and its use, and finally related expressions and how they differ. For the JLPT, I find the differences section and the example sentences the most helpful. The quality of the example sentences is excellent (they are nearly all examples of real world use) and the translations are first rate.
Romaji and furigana are provided for all sentences in the first two volumes, and furigana is provided for all but the easiest kanji in the third volume.
All books contain a somewhat useful introduction, and the second volume includes a thorough set of appendixes, my favorite of which includes an extensive list of compound verbs, each with their meaning and then several example sentences demonstrating their use.
To buy all three books is quite expensive. If you're short on money, and already have studied Japanese a few years, you can safely skip the first volume. The second one is very valuable for its appendixes, and if you're studying for the JLPT 2 it's the most important, though many JLPT 2 terms are also covered in the third volume (and a few in the first).
If you're studying for the 1kyuu, the third volume is the most important, but unless your 2kyuu grammar is perfect the second volume will probably help a lot too. The example sentences are often quite challenging and very instructive, even in the early volumes.
Unfortunately, since the third volume was just published recently in Japan, it probably hasn't reached US bookstores yet. However, you can order it from Amazon Japan (see the link on this page).