I have found this small [23 pages] book to be invaluable as I had a poor public school education in English grammar with many gaps in my understanding. I got my first copy for $3 at a seminary bookstore after a recommendation from an instructor for a New Testament Greek course. I have given several copies to family and friends over the subsequent years. Typically can be found at university bookstores or Amazon, etc.
English Grammar for Language Students: Basic Grammatical Terminology Defined and Alphabetically Arranged
Frank X. Braun
I have that book and it's excellent. When I do have a question I can't find the answer to online, I'll either go there or to my trusty (and dusty) copy of Strunck & White's The Elements of Style. But truth be told, most of the resources I use are online. This site is particularly useful, but there's many you can trust.
I have the OWL site in my Firefox bookmarks but had forgotten about it. That tends to happen to things that I bookmark.
Some others I have used:
http://www.cws.illinois.edu/workshop/writers/
Grammar Handbook
https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style
The Manual of Style is the style manual for all Wikipedia articles
http://www.grammarly.com/handbook
Grammarly Handbook
http://andromeda.rutgers.edu/~jlynch/Writing/
Guide to Grammar and Style
http://andromeda.rutgers.edu/~jlynch/Writing/links.html
Resources for Writers and Writing Instructors
http://www.usingenglish.com/glossary/
Glossary of English Grammar Terms
The Chicago Manual of Style Online [except for Browse Q&A section] and AMA Manual of Style both appear to be subscription-based.
Oxford Dictionaries Online - Grammar and Usage is succinct, while Grammar Monster is more lengthy. Both are useful.
Thanks. I added both to my bookmarks.
Now I just have to not forget they're there.
I just found at Half Price Books on clearance for $1.00Â Simon and Schuster Handbook for Writers.