I've used prweb before and I think it's one of the more effective press release services out there. In all the times I've used it, all of the releases on prweb's partner sites were indexed by Google and other search engines within a day or two. It really has actually helped in boosting my search engine rankings.
You can also do it the old fasioned way and send your PRs to local newspapers, magazines, television, and whatnot. You might find a local paper to pick it up.
You may want to have a look at the thread below. The bulk of their service comes from writing the press release, but I contacted Danny a month or so back asking if he did distribution, by itself. His answer was of course, yes. I haven't used Danny's services yet, but I will be doing so in the coming weeks.