The Zack Company, Inc.,a literary agency, is actively seeking clients. In the past, the agency has stopped accepting queries at different times (because of slush pile overflow, most likely).
As far as I can tell, the agency is looking for all kinds of nonfiction, and some fiction. Regardless, this seems like a great opportunity.
The agency's Web site has an incredibly detailed "What We Want" page detailing what to send and how to send it.