PR the old kind not Google Page Rank. Is a great tool and always has been. The tricky thing is working out the impact of it and assigning return on investment on it. I'm a direct marketer at heart and like to know how much I'm paying for my responses and how much I'm making.
Traditional PR has never been able to provide that. It's always been a finger in the air measurement. However web based PR changes all that. When someone reads your Press Release they can do an number of things to spread it, blog it, link to it and even come straight to your site. Over on Online Marketing Blog they've kindly listed a whole bunch of great resources for online PR.
For my two pence worth, the best way is to work long and hard and build strong relationships with key players in your niche. But you have to start some where and the online distribution areas are a perfect place