Complete French Grammar is by far my no. 1 pick for students. It's the most popular grammar book on the market and would make for an excellent accompaniment for any online class!
French Grammar For Beginners
is a wonderful option for self study for pure beginners who have never learned any French before. Great place to get off to a good start!
My next favorite is the Complete French Grammar Course. Also great for self study, this is book is a bit more comprehensive and goes a further in depth than the previous book. I also love the audio!
I'm a huge fan of the Grammaire En Dialogues series. These books offer wonderful dialogues and do a great job mixing formal French grammar with modern French as you'd hear it on the street.
This is the palm-sized Barron's French Grammar book. It's small but packs a powerful punch! Very comprehensive coverage of all aspects of French grammar. It's an essential reference for all students.