Fiction Genres

FictionDB: The Essential Fiction Reference
Free resources include the ability to search for mysteries, westerns, and romances, etc., booklists, and book reviews of new releases.
NoveList
A database provided by Torrance Public Library provides enhanced subject access to over 74,000 fiction titles for all ages. Explore genres by clicking "Start" then selecting "Explore Fiction." Access is available from home and work for this database. Instructions are available at all library facilities.
Overbooked
Overbooked specializes in literary and genre fiction information. Includes author web pages, annotated lists of books, and themed booklists.

Classic Literature

BookSpot
Provides links to full-text classics.
Classics Pages 
Ancient Greek and Roman poetry and literature.
King Arthur 
Comprehensive exploration of the legend.
Online Medieval and Classical Library
A collection of literary works from Classical and Medieval civilization. You can search by keyword across texts.
Perseus Digital Library
Links to e-texts and other information about Classical literature.
Project Gutenberg 
Over 6,000 public domain titles, many classic literature.

Horror

Horror Writers Association
Services for horror readers including a reading list.

Mystery

Librarians' Index to the Internet Subject Guide for Mysteries 
A guide to booklists and bibliographies, famous characters, history of the genre, author interviews and more.
Mysterious Home Page
A collection of links to the mystery world online.
Mysterynet.com 
Online mysteries, mystery games, mystery books and resources for everyone who enjoys a mystery.
The Mystery Reader 
Hundreds of book reviews for your mystery reading pleasure searchable by sub-genre. The site also includes author interviews, freebies and much more.
Stop, You're Killing Me!
A resource for readers of mystery, intrigue and suspense books.

Romance

All About Romance
For and by romance readers.
Romance Writers of America
Provides definitions of romance types, reading lists and statistics.

Science Fiction & Fantasy

Los Angeles Science Fantasy Society 
"The world's oldest continuously active science fiction clubs"
Science Fiction and Fantasy Writers of America
Lists recommended reading.
Science Fiction Resource Guide
A good starting place for a variety of topics.
Technovelgy.com
"Explore the wide variety of inventions and ideas of science fiction writers."

Westerns

Western Writers of America
This list of best westerns includes novels, non-fiction and films.