Just eight weeks ago, Seattle-based Farecast introduced a new online service that allowed travelers from Seattle and Boston to see if airfares between those two cities and about 60 major destinations would be going up or down in price in the near future.

The service attracted a lot of attention, including a plug in Time as one of the "Top 50 Coolest Web sites of 2006" and mentions in The New York Times and Wired.

But travelers in other cities wanted in on the action, with more than 50,000 people signing up to be notified of the national launch. Today, partly due to that buzz, Farecast is unveiling its airfare prediction service for more than 55 cities, including New York, San Francisco and Chicago. The launch comes a few months ahead of schedule, something that Chief Executive Hugh Crean said they pushed forward because they were "thrilled" with the initial attention it received.

"It was a local launch in a couple of markets, but it certainly garnered national blog and media attention," said Crean, adding that the site has already attracted more than 200,000 visitors.

In addition to the national launch, the company has added advertising through Yahoo and RSS tracking so that people can keep tabs on changing prices of flights.

Here's more on the national launch from GigaOm and The New York Times. And here is my story on Farecast from May when the company first unveiled its service in Seattle and Boston.