While the most popular press release sites are paid and take a fee to post a press release, there are many press releases that you can submit content to and get a backlink from.
To get the best out of press releases, try to publish a newsworthy story. That way not only will you get a link from the press release site, but news publishers and people looking for news in the niche may pick your story up and publish it on their sites with a link back to you.
Press release sites are one of the few places where your links can go viral.
Here’s a list of free press release sites: http://mashable.com/2007/10/20/press-releases/

