Writers and Artists Yearbook is the trade bible in the UK, but it does list agents and publishers in the US, and those publishing houses based in both countries (and others besides). It gives a precis of what each agent/publisher accepts and also gives guidelines on how to submit.
Link here:
http://www.writersandartists.co.uk/
One word of warning - unless you are knowingly self-publishing, you should not have to pay any agent or publisher up-front. Beware, because anyone can pay to be listed in WAYB.