Evan Carmichael at the Young Entrepreneur Blog has five secrets for how a start-up can generate PR. I like that these tips aren't very work-intensive. They're fairly simple things that a one-man operation could implement. You don't need to hire a PR agency. I'd emphasize one of his secrets, and then expand on another. Emphasis on this:
Bloggers and reporters are some of the busiest people you could possibly hope to meet. They're actively looking for the most interesting, relevant, and linkable stories out there, preferably before anyone else can run with it. But truthfully, they spend most of their time hacking through the weeds of generic or over-the-top inbound emails, press releases, Facebook messages, Skypes, SMSes, Tweets, and IMs. It's almost a small miracle that anyone can ever get their story told.
My inbox is often mobbed with press releases that sound pulled from a generic company bio. In an outreach to a journalist, if you can lead with just one sentence that explains how your start-up is indicative of some kind of trend, you are 10 times as likely to get attention.
I would add that the influence of blogging oneself should not be overlooked. I've found several interesting start-up stories by scouring Technorati for entrepreneurs who are writing about their issues and problems. I would guess most people who are likely to give online public attention to a new start-up do similar things. Blogging might seem like a time-consuming thing to do, but it doesn't have to be. You can register with Technorati, write just one or two blog posts about some problem, and write a headline with keywords that would make your post pop if someone was searching for a particular issue (like, say "Entrepreneurs and Start-up Financing").