Writing a press release, sending it out for distribution, and having it get picked up and written about are all separable (and important!) elements to doing this "right". If you have not actually done this before, I would recommend working with somebody who has some level of experience with this in tailoring your overall PR strategy. In any case, in direct answer to your question, three services that come to mind for sending out your press release for you include:
I have no association with them, but if I had to recommend one of the above, getting a sense this is a new thing for you, I would probably suggest Send2Press as the best of the three for you. They are pretty cost effective and can provide quite a bit of value add in helping to make sure you are targeting things in a way that will really get picked up better. ie: If you just blast out your release to everyone, and the writers realize this, they tend to blow it off because they are looking for a hook and a unique (as possible) angle for themselves.