Here some more: ereleases.com/ softpressrelease.com/ prndirect.prnewswire.com/ send2press.com/ submitexpress.com/press_release.html free-press-release.com/ emediawire.com
Yes, they're enough as far as press release distribution sites go. Don't waste time submitting to a lot of free sites - most of the traffic you get from them won't stick around or convert, and most of the backlinks are of poor quality (they'll soon be buried on archive pages or they're from scraper sites). Only post to distribution sites that will directly reach your target audience (for example, PRweb can be fine if you're targeting bloggers), and to get into search results in news engines like Google News or Yahoo! News. Spend the rest of your distribution time manually targeting a few key websites, blogs, or offline media outlets that may have an interest in your story. If you have real news, a quality press release, and you've distributed it effectively, you can get some nice exposure, high quality links, and targeted traffic - but you'll never realize the full potential of news releases without all three of those elements.
Is PRweb.com free to use or only free to register? That is, after I register free, do I have to buy anything in order to post a press release?