I've noticed that many editorial websites are also adding email distribution to their stable of advertising services, and I could readily see these sorts of ads moving to the email realm, where particular email newsletters that are targeted at specific audiences, would be a great way to get the word out.

So, the Union of Concerned Scientists could target legislators by sponsoring a particular day's worth or week's worth of daily email newsletters, with their message.

I think there's great opportunities online, though the general-media sites like city newspaper websites will have to get more aggressively into email newsletters to take advantage of some of them.