So, a bit of a shameless plug here, but this is the kind of thing that makes our jobs easier! Marketwire (competes with PRN and Bizwire) is a GREAT service. It's cheaper than PRN and Businesswire, and it has better service, and some really cool extras that the other wires aren't even close on (to my knowledge at least). Below, my acct person Nick breaks it down in detail, but net net, here's why you might want to consider using these guys:
For like $50 or so, they do a search optimization on your press releases that can take you from no listings on google searches to being on page one. Huge! For around $100, you can embed video (YouTube style) into press releases, which then get disseminated to all of the outlets that run video. Lastly, they are connected to sites like Digg and Delicious... if you haven't heard of these, check them out... they are the next wave of how we consume news/do searching, etc.
Super forward thinking, and not too expensive. Just wanted to share the love.