I tested out a news release service today, one that offers free online PR releases. You can read my press release here: How to Create a New York Times Bestseller.
You can create and promote your own free online press release at http://www.prlog.org as well.
I also joined BookCatcher.com and posted a news release there, but I'm not sure if it will be posted. Apparently someone there reviews news releases before they get posted, so it's not automatic. Check out Book Catcher.
For a list of other free online PR services, see http://www.bookmarket.com/onlinepr.htm.