If you're looking for a clear, basic overview of grammar in audio format (with written exercises to boot), consider Leonard Peikoff's Principles of Grammar course.
I received the audio-tape set as a gift years back and truly enjoyed it. Peikoff presents the lectures as grammar lessons for writers, explicitly excluding matters of style (which vary from publication to publication) and more in-depth grammatical analysis. He provides a good summary of grammar basics and addresses ways to adjust your writing's structure or diction to elicit various rhetorical effects.
Very worthwhile -- for a writer or an editor.