I highly recommend Herman's book too. It's jam packed with agents and publishers. Buy it, read it, and highlight any of them that might be a perfect fit for your book. Then go back and start submitting.

Dianne's suggestion is also an excellent one. I did that while trying to find a publisher and agent. Just go to the book store or library. Find all the books that are similar to yours. Look through the acknowlegement section. They will always mention their agent, especially if he/she is good. Write down the book title, publisher, and agent. Go home and start researching online. Then send your query to all those people. Be sure to mention how you learned of them. It sets you apart form all the other queries they receive.

Publishers and agents represent very specific subjects. You can't query one who sells women's issues if you are trying to market a book on sports. It's a waste of time.

Just because you are rejected doesn't mean your work isn't good. It means it isn't a perfect fit for that agent, or publishing house.