PR Web- One of the main PR sites that can really build your brands name out there along with adding backlinks to the site. You need to sign up for their better packages that have SEO built into it, but its worth doing at least once. Here is a link for 10% off your first Press Release.

24-7 Press Releases- This is another press release site I've used in the past. Very similar to PR Web, its just a preference, unless you really want to cover your ground, use both.