In no particular order:
American Heritage Dictionary, College Edition
Funk and Wagnalls Dictionary (1964)
Webster’s Collegiate Dictionary, Fifth Edition (1936)
Oxford English Dictionary
Chicago Manual of Style, 13th Edition
Brewer’s Dictionary of Phrase and Fable
Collegiate World Atlas (c. 1968)
Quirk and Greenbaum, “A Concise Grammar of Contemporary English”
Columbia Desk Encyclopedia
The Complete Guide to Primetime TV Shows, 1946-Present (C. 1975)
Partridge’s Dictionary of Slang
Bartlett’s Familiar Quotations, 15th Edition
New York Times Desk Reference
GPO Style Manual
Skeat’s Etymological Dictionary (c 1882)
French, German, Russian, Italian and French to English dictionaries
Capricorn Rhyming Dictionary
The Word Book
AP Stylebook
Medical Dictionary
Fowler’s Modern English Usage
What’s What
Follette’s Modern American Usage
Descriptionary
Oxford Companion to the English Language
Various Almanacs
The Rock Encyclopedia (Roxon)
Halliwell’s Film Guide (c. 1970)
Encyclopedia of Rock
Horne’s “The Comic Book Encyclopedia”
The Great Movie Stars (2 volumes)
The Science Fiction Encyclopedia
The Encyclopedia of Science Fiction (just to show off my entry)
The Baseball Encyclopedia
The Home Run Encyclopedia
The Sports Encyclopedia: Baseball
The Enclopedia of Baseball (Turkin & Thompson)
The People’s Almanac
The Book of Lists 1, 2 & 3
The Encylopedia of Comic Book Heroes, Vol. 1, Batman
Listening to America
Panatti’s Extraordinary Beginning
Panatti’s Extraordinary Endings
The Fifty Worst Films of All Time
The Golden Turkey Awards (I and II)
Hollywood Hall of Shame
The Mot Juste
NY Public Library Book of Answers
Strunk and White
The Transitive Vampire
The Well-Tempered Sentence
Hammon Almanac 1979
Guiness Book of World Records
The Pocket Book of Quotations
The Straight Dope
More of the Straight Dope
Maltin’s Film Guide 1994, 1999, 2003
And plenty more. You can’t have too many reference books.