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.