I've done very well using press releases and offline publicity in general to drive targeted traffic to my websites - just wrote an ebook about it, in fact.
There's a whole section devoted to how/where to post a press release online and different sites are better for different needs. For example, some are much more helpful for online marketers in that they offer hyperlinked text and keep your press releases archived longer (in a non-password protected area, so that search engines can find them.)
It IS largely true that you get what you pay for, when using press release distribution services, but a couple free sites that are well-regarded are:
http://www.prleap.com
http://www.openpr.com
http://www.pressreleasespider.com
http://www.pr.com
http://www.i-newswire.com/
http://express-press-release.com
Free press release distribution sites tend to change often, and policies change - also note that while a submission may be free, you may have to contribute money to get any kind of visibility.
Diana Ratliff
http://www.PublicityTrafficSystem.com
Use the power of FREE publicity to drive targeted traffic to your website!