Working with an Agent is the only way. As I have understood from reading Bob Mayer's book, called "The Fiction Writer's Toolkit", which covers the ENTIRE publishing process in the second half of the book, getting a book agent (and being patient with the process) is the proper (and only) way to get the attention of a publisher. As you will notice from reading this page on Random House's website (
Random House - Contact Us) they state, as the Bob Mayer confirms in his book, that most serious publishers (which are the only ones you should be inerested in) only deal with agents... not authors, or directly submitted manuscripts that you want them to review.
But fear not. Agents don't cost you a thing from your pocket, until AFTER the book is published (usually taking a flat-rate of 15%). Some may see this as a slight annoyance, but you
should be very, very grateful; it's either 15% of what you make, or no book, because agents
are the publishing process, as far as any author in the world is concerned. There's no other way to know how to deal with a publisher, and real publishers only deal with agents, as stated on Random House's "contact us" page.
When I copyrighted my book, I started getting junk mail from Dorrance Publishing, but I only took a brief look at their website before realizing they were small-time and probably unsafe. As mentioned in Bob Mayer's book, if the publisher is seeking you out, you know something is very wrong. A "real" publisher does the opposite, and lays low, waiting only for an author serious enough to study the process, and get a proper agent. Those are who they work with, and who get a good shot at getting published, if their book is good.

In all normal circumstances, the publisher is the one who pays YOU an advance at contract-signing... not the other way around. Nothing ever comes out of your pocket in the entire book-writing/publishing process.