Haven Books
A general used, rare and out-of-print bookstore; hardcover books with an emphasis on non-fiction, including antiques, military, railroad and aviation. Based in Winter Haven, Florida.
http://havenbooks.org/

Haymes and Sons
Catalogue includes art, architecture, travel, exploration, military, natural history, sport, theology, fashion, theater.
http://www.haymes.com/

Henry Hollander, Bookseller
Antiquarian and scholarly bookstore specializing in Judaica.
http://www.hollanderbooks.com/

Here Be Books
Full-service used bookstore. Used, rare, and out-of-print books and collectible roleplaying games (RPGs): hard cover and paperback. Search service. Brodart book covers.
http://www.herebebooks.com

Heritage Books
Rare and hard-to-find books in many categories; also ephemera.
http://www.heritagebks.com/

Hidden Staircase
New collectible and out-of-print books, as well as gift items.
http://www.hiddenstaircase.com/

High Ridge Books
Antiquarian and used books.
http://www.highridgebooks.com/

Hillside Books
Books on insects and related topics.
http://www.insects.demon.co.uk/

Horizon Books
Travel, voyages, exploration, natural history and gardening; rare, used, antiquarian and out-of-print books.
http://www.horizonbook.com/