I respect the fact that books are expensive and that students are too often required to purchase books that they don't use either enough during a course or after the course is over. That having been said, the books I list below were chosen because they will serve you now and years from now as well. I had most of them above my desk in my own classroom; and they are all still in my bookcase at home--referred to often.
The Rise and Fall of English by Robert Scholes
They Say/I Say: The Moves that Matter in Academic Writing by Gerald Graff and Cathy Birkenstein
On Writing Well by William Zinsser
The English Teacher's Companion by Jim Burke
The Grammar Plan Book by Constance Weaver
Creating Writers Through 6-Trait Writing Assessment and Instruction by Vicki Spandel