Attempt to find an agent. Sometimes it is as hard to find an agent as it is to find a publisher. You can find a listing of literary agents in the "2010 Writer's Market." Follow the guidelines laid out by the agency. Most prefer receiving a query letter and not a complete manuscript.
Contact publishers. You can submit your manuscript to some publishers without going through an agent. The "2010 Writer's Market" contains a list of publishers willing to look at non-agented works. A query letter or proposal package with sample chapters is usually requested. Only send a complete manuscript if the publisher requests it.
Self-publish your book. Many very good books are never published by traditional publishing houses. Your only alternative at this point is self-publishing. You can have a printer print several copies of your book, or you may submit your manuscript to a print-on-demand publishing company, which costs much less.