I knew about a couple of these, but it's handy to have a list in one place... the old-fashioned slushpile is not completely dead!
http://www.authorspublish.com/12-imprints-of-big-5-publishers-open-to-unsolicited-submissions/
http://www.authorspublish.com/12-imprints-of-big-5-publishers-open-to-unsolicited-submissions/