Two nice things for you on the main mb page. Rachel Kramer Bussel speaks to Peter Lynch, Senior editor at Sourcebooks:

Can you give me an overview of what kinds of books Sourcebooks publishes (under its various lines) and who your target audience is?
Sourcebooks publishes in almost every category. Our Sourcebooks imprint is mainly comprised of nonfiction, in such categories as business, gift, beauty, reference, politics, history, parenting, college guides and study aids, poetry, real estate, self-help, relationships, humor, sports, and pop culture. Our Sourcebooks Landmark imprint publishes a select list of literary and commercial fiction; Sourcebooks Casablanca publishes books on relationships and sex; Sourcebooks MediaFusion produces book+media (such as CD) projects that bring experiences to the reader; Sphinx Publishing publishes legal self-help guides; and the new Sourcebooks Jabberwocky is our entrance into the children's market, led by New York Times bestseller Poetry Speaks to Children.

I acquire almost entirely nonfiction across many categories, with a particular focus on college guides and study aids, business, reference, sports, humor, pop culture, and history. You never know what type of book can end up on my list.

Read more here. Also, check out How to Pitch: National Geographic Traveler.