Over at Entrepreneur Magazine, Mark Cuban has listed 12 interesting rules for Startups, including a rather jaded view of PR.
Never hire a PR firm. A public relations firm will call or email people in the publications you already read, on the shows you already watch and at the websites you already surf. Those people publish their emails. Whenever you consume any information related to your field, get the email of the person publishing it and send them a message introducing yourself and the company. Their job is to find new stuff. They will welcome hearing from the founder instead of some PR flack. Once you establish communication with that person, make yourself available to answer their questions about the industry and be a source for them. If you are smart, they will use you.
You can read more of Cuban’s lessons in his book, How to Win at the Sport of Business: If I Can Do It, You Can Do It.