For one, personal contacts ALWAYS trump blind press releases. Therefore if you want to spend some money spend it on actually attending conferences (GDC etc) and try to get in contact with the journalists.
The easiest way imo is through twitter. It may take some time but if you follow their conversation and get to know them (just DO NOT PITCH YOUR GAME...EVER on social media if you try to get in contact with someone or make friends!).
In my experience blind press releases to the big guys are just wasted time and effort.
What you should do is target smaller blogs (http://www.pixelprospector.com/
comes to mind.
I did a small test earlier this year where I did send the same press information to the big guys (Kotaku, RPS, IGN etc) but also to a few smaller indie blogs (http://www.pixelprospector.com/
). The big ones didn't cover the news but a few days later pixelprospector write about it and low and behold the big guys picked it up from Pixelprospector directly.
So it's a good idea to make a list of sites/blogs that get picked up by the big guys. Once THEY cover your game, check WHO covered it and try to get in contact through twitter or email. A thank you for the coverage is also always a nice opening to establish a proper contact.
Specially the big guys won't really respond to your emails even if they go on covering your future PR. If you have met them during a conference though, that's much more personal and you always have something to fall back onto.
Indie Marketing = Making Friends
AAA Marketing = Paying Friends
Now, which of the two friend types is most likely the more loyal?
Not to mention personal contacts also show the journalist the person or studio behind the game. And last but not least, you are always much more inclined to believe a friend/someone you know than a random stranger without a face.