I wouldn't necessarily recommend
textbook textbooks, but something like A Dictionary of Basic Japanese Grammar is always a good one. And, you can't live off that and J-pod alone either. You need to get a heavy stream of made-for-native (not made-for-learner) material. Past the very beginning (possibly from the beginning), your made-for-native material should have be on the high side of your native-to-learner ratio. It runs counter to the attitude we're usually instilled with, but actual skill (and knowledge) is gained through actual doing, and learning materials and classes and coaches are
support, not the main resource. Like a guideline, tips. Like when you learn an instrument, you study scales and shit, but the biggest thing is to go play some songs, harder and harder all the time. When you learn to draw, you pick up books on techniques and anatomy studies, but the biggest thing is to just draw everything.
Of course, actually
doing Japanese means a lot of guesswork (as described in the Rosetta Stone complaint), but so does gaining ground in absolutely any other skill. Massive confusion is just part of the process. But it's a lot more fun when it's not Rosetta Stone