S & L New and Used Books: Used books of all types in numerous categories with thumbnails.
Sage Old Books: Modern first editions, author signed books, Australiana, plus wide range of 19th and 20th century used books.
Sangraal Books: Used books, in browsable categories, including fiction, philosophy and fantasy.
Sassy's Hide - A - Way: Many categories of books including; mystery, romance, children's, educational, and novels.
Savoy Books: Specializing in horticulture and agriculture, historical Americana, English and American literature.
Schwartz Judaica: Out-of-print books of Jewish interest from art to Zionism, in various languages, including English, Hebrew, Yiddish, and German.
Scrinium Classical Antiquity: Secondhand and antiquarian books on classical antiquity. Online catalogues available.
Sean Fagan, Rare Books: Book seller offering a searchable database and photographed catalogs of scarce books in many fields.
Seasoned Books: Specializing in books on sustainable lifestyles, wilderness adventures and renewable energies.
Second Life Books: Antiquarian and out of print books by and about women, first editions of literature, agriculture, and horticulture; a range of printed and manuscript material from the 16th to the 20th century.
Second Story Books: Used books; Mystery and Science Fiction catalogues issued regularly.
SeekBooks.co.uk: Used and hard to find books; browsable and searchable site.
Serendipity Books: Used and rare books; based in Berkeley, California.
Serendipity Books: Used, rare and out of print books. Specializing in nonfiction including science, history, religion, and social sciences; based in Michigan.
Sheila Markham Rare Books: The East; exotic printing, calligraphy and general antiquarian books.
Sigler Press: Out-of-print books about Biblical studies, theology, church history, and pastoral care.
Signed Books: A collection of new books that have been signed by the authors.
Signed Rare Books: Signed rare books, modern first editions and antique books.
Significant Books: General books, also with a specialist interest in science and technology.
Simpson Books: Specializing in modern, out-of print, first edition collectable books, many signed by the author.
Skriptoriet Used Books: Scandinavian used and antiquarian books and online entry of book location requests. Bilingual, Swedish and English.
Sleepygirl's Used Books: An internet only used bookstore.
Slightly Read Books: General stock open bookstore in Grinnell, Iowa. Searchable, browsable site.
SS Enterprise Books: Includes archaeology, history, fiction, military, and royalty.
Stackstreet Books: Rare literature, first editions, poetry, science-fiction, graphics, New Zealand.
Steve the Fish: One man business selling first editions and collectable books.
Stone House Books: Specializes in modern first editions, collectible children, science fiction, horror, mystery and Edgar Rice Burroughs "Tarzan" books.
Straight Arrow Publications: Used, rare books, and first editions. Includes reviews and links, specializing in historical matters; also has Native American genealogy.
Studio Bibliografico san Mamolo: Specializes in old and used books about nature, science and history. Also in Italian.
Sumner and Stillman: Antiquarian Booksellers, specializing in nineteenth century British, Irish and American literary first editions.
Sunbow Books: Used books searchable by author, title or keyword.
Symposion Books: Auction hall and online antiquariat.