A Dictionary of Basic Japanese Grammar
The Dictionary of Japanese Grammar series (there is also an intermediate and advanced book) is a must for every Japanese learner's bookshelf. This book covers about 200 grammatical phrases and constructions--all organized alphabetically.
Have a question how to properly use ~tara? Look under "T." How about "koto ga aru"? Look under "K."
Just about any grammatical construction a beginner will come across has an entry.
In addition, there are extensive articles on word order, particles, pronouns, passive voice, politeness, and much more.