
Ghosts and Scholars : Rosemary Pardoe's acclaimed journal of fiction and commentary, chiefly concerned with things in the style of the Master, Montague Rhodes James.
For serious readers, book collectors and researchers of the Macabre I can think of no better notion than a visit to Professor Voller, at The Literary Gothic Page
For the best in Science Fiction and Fantasy, see The SF Site
The Dreaming: Neil Gaiman's Home Page puts you in the Sandman's realm.
The Terry Pratchett Home Page Ah yes, the Discworld, where the Librarian peels bananas with his toes, Death is just a tone of voice (but a unique tone of voice), and Cripple Mr. Onion is really the only game in town...you owe it to yourself to enter the Century of the Fruitbat!
The Patrick O'Brian Home Page will get you to the Holy Windward Side of the Quarterdeck;
Helen Murphy's Searoom-L Listwains' Map will show you where the dedicated followers of Jack Aubrey and Stephen Maturin, et al maintain our harbors, while
Gibbons Burke's Ultimate Patrick O'Brian Page has gathered every POB link imaginable, including the Nautical Idiom List and Music Index to the Aubrey-Maturin series: Tally and Belay!
For an excellent overview of the genre generally, check out
John Kohnen's Nautical Fiction List
The BookWeb(tm) Home Page from the American Booksellers Association, collects sources as well as ever it can,
The BookWire - news and views from inside the publishing business.
Project Gutenberg has been around since 1971, and is no less than an attempt to put every book in the public domain online - well worth a browse
inkygirl - one of lots and lots of writer specific blogs - is a good writer's resource, as is
The Children's Writing Resource Center
The Library of Congress might have what you can't find in the house!
The Internet Book Information Center is also worth a read.
Or check out the New York Public Library Resource Guides.
I am a veteran of many years' bookstore employment: Bookstop, Brentano's - and I've long toiled at this fine spot: Half Price Books
The Internet Book Shop (UK)
@Random:Random House Publications 
HarperCollins Publishers - among my favorites, along with
WW Norton 
Alibiris and Abebooks - the Internet's prime search sites for old, used and rare books.
Justin's Links to the Literary
The New York Review of Books
Booklust
LNR
Identity Theory