While using an agent to get your book published will increase your chances, an agent will cost you about 15 percent of your earnings. Many beginning authors aren't willing to pay that much money from their first earnings. Even if you are willing to pay the percentage, it's often as difficult to interest an agent in your book as a publisher. Most mainstream publishers do not accept unsolicited manuscripts anymore, but there are a few notable exceptions. Some welcome them as a means to discover exciting new writers.
Baen Books is a science fiction and fantasy publisher. It accepts unsolicited manuscripts for all books and prefers electronic submissions through its manuscript-submission form. Baen is very accepting of new authors and has a large e-publishing department.
Boyds Mills is a publisher of children's and young adult books that accepts unsolicited manuscripts. It is looking for fiction, nonfiction and artwork submissions. It prefers submissions by regular mail, rather that email, and says it will respond within three months.
DAW Books is the science fiction and fantasy imprint of Penguin Books. It accepts unsolicited manuscripts from beginning writers and prefers them in paper form. It says it will respond in about three months and will not consider manuscripts that are under submission to other publishers.
TOR Books (see Resources below) accepts unsolicited manuscripts on a variety of subjects. It is looking mostly for paranormal romance, mainstream and women's fiction, science fiction or fantasy, chapter books for children and young adults and horror. Manuscripts should be mailed, no query letter required.
Lee & Low Books
Lee & Low Books (see Resources below) publishes books for children and young adults with a multicultural theme. All manuscripts must be aimed at children of color, with an authentic voice. Submissions are accepted from new authors through regular mail; no email submissions are accepted. .