BTW, these companies are US based. Try to find one that is closer to you if you live in another country. You’ll have a better chance publishing where you are first than in a foriegn country. Good luck!
Slave Labor Graphics
For more lists of publishers, check out our Resources page.
For words of wisdom, check out Scott Frazier’s page: Jobs in Manga.
Another option to getting published to try out for contests such as TokyoPop’s Rising Stars of Manga Contest. Started in 2002, this is a contest that has grown from US-only submissions to now include the UK. Winning submissions get prize money plus get their work published in a compiled volume called, of course, “Rising Stars of Manga”. Besides getting prize money, publication, and name recognition, you can pitch them a story.