My favorite genres include:
***Language/Etymology/Lexicography **(Safire, Lederer, Estes, Ciardi)
***Mystery **(Light and Cozy, no gore)
***Classics **(I’m working my way through a list of the top 100 books of the Century)
***Vanity Fair Magazine ** (a guilty pleasure!)
And based on a recent thread, I’m going to go back and reread Beverly Cleary!
Humor. (be it Dilbert or PJ O’Rourke. Well done is just that.)
Travel stories. Travel Guide Books.
Straight Dope and trivia books.
The meaning/origin of books.
Biographies ( preferably the micro condensed versions like the Great American Bathroom Book types.)
Eyewitness Guide to: animals, stars and planets, gemstones, et al. I love these books.
Children’s lit.
The works of Eve Golden. 
Books that I want to by all varieties on the book store shelves for myself and cannot really *explain * exactly why: baby names books, dictionaries and thesauras’ ( or is it: thesauri?). If i ever get this way about Catcher in the Rye, someone please shoot me.
I’m a geek. I have an AT&T 4 ESS operator manual next to my throne for a little light reading. I also read other technical manuals.
Sci-fi/fantasy.
Non-fiction science, especially aerospace or astronomy related.
H.P Lovecraft type horror
Religious texts and books about religion.
Anything else I can get my paws on.
I like:
jessica
I read anything. Right now I’m tackeling Zen and the Art of Motorcycle Maintenance. If I just want to read for fun, I head for mystery first. The Cat Who… books by Lilian Jackson Braun are beautiful, fun books and I crave Dorothy L. Sayers on a regular basis. I also like fantasy a lot.
How did I forget? I read cook books more than anything else. Cook books, books on the history of food and wine, on the scientific priciples behind cooking, essays about food and cooking. You get the idea.
Anamorphic, if you like hard-boiled detective novels of the 1930s, do a search on a used-book site for Tiffany Thayer. He was so hard-boiled you could roll him on the White House lawn!
Another dilettante, here. I try to browse in different areas of bookshops every time, and will usually come away with a nice mix of stuff from Cookbooks, African-American Studies, Eastern Religions, Poetry, Chess, Miltary History, Reference, Science Fiction, whatever.
I like poking around the Modern Library racks in the Strand Used Bookstore…a great and eclectic old imprint. Last time I ended up with an anthology of Irish poetry, A Treasury of Damon Runyon, Gogol’s Dead Souls, the complete plays of Kaufman and Hart, and The Sex Problem in Modern Society.
Mysteries - both cozies and hard-boiled ones.
Non fiction - criminal psychology, forensic investigation, true crime (though not the pulpy, trashy ones)
And cookbooks!
Never heard of him. Thanks for the tip! I will definitely seek him out! Especially after such a great analogy. 
Anamorphic, I especially recommend Thayer’s 13 Men, 13 Women, and Call Her Savage. I’m sure you can get cheap copies on bookfinder.com.