Randolph Quirk et al. A Comprehensive Grammar of the English Language Longman, 1985, ISBN 0-582-51734-6
Otto Jespersen A Modern English Grammar on Historical Principles
7 volumes, Heidelberg: Carl Winter, 1909-1949
These are no doubt excellent recommendations for the serious student, but for the
dilettante they are serious overkill. The Quirk book has 1799 pages and sells at
Amazon.com for $167.99. The Jespersen work is out of print and it is apparently
nearly impossible to find a used copy. (I've been trying to get a copy through
various bookfinders for a couple of years now with no success.)
The less serious student looking for a good English grammar reference could
do worse than to find a copy of A Dictionary of Contemporary American Usage, by
Bergen and Cornelia Evans. Although it's an alphabetical listing of English-usage
topics, it's also a good reference on all of the fundamentals of traditional
grammar. The authors say in the preface:
[The book] also contains a full discussion of English grammar, a discussion which does not assume that the student can already read and write Latin.
If any reader wants to make a systematic study of English grammar he should begin with the entry parts of speech and follow through all the main cross references.
This book is also out of print, but I have seen copies in used book stores.