While I was at BEA, I met Drew Gerber of Pitchrate. And the minute he described his service, it made complete sense to me. Through Pitchrate, experts and authors can get in touch with journalists and PR folks who are looking specifically for certain stories or expertise.
These journalists or PR people send out requests every day for experts, and then you can respond with a pitch. It’s very simple - and the Pitchrate tools seem pretty easy to work with; highly email-based (although there seems to be a web app you can use as well). Journalists rate the experts they talk with, so if you’ve achieved a high rating, chances are other journalists will be in touch!
I think these services are very useful, particularly for nonfiction writers who are steeped in certain topics and have a specific message to get out. So check it out!