Felicity Books
Second-hand, used books for sale on-line. Categories from the rare, spiritual, crime, and fantasy.
http://www.felicity.com.au/

Fine Print
selected books for antiquarian and rare book collectors and many special interests.
http://www.afineprint.com/

Finn's Fine Books
A catalogue of facsimile books (exact replicas) of old manuscripts, Leonardo's works and other limited edition books.
http://www.finns-books.com/

Flatsigned Books
Specializes in signed first editions.
http://www.flatsigned.com/

Foundling Books
Specializes in children's books, particularly Boy Scout and Disney related items. Also used and rare books on a wide variety of other topics.
http://foundlingbooks.com/

Frank & Carol's Books
Secondhand books, categorized by author and subject. Based in Norfolk, England.
http://www.ashbook.co.uk/index.htm

Frogtown Books
Used, rare and out-of-print books and autographs in a variety of categories.
http://www.frogtownbooks.com/