Watch out Apartments.com, Rentals.com, Rent.com, ApartmentFinder.com, MyNewPlace.com and every other Web site where people go to find a place to live. Here comes the Zillow.com juggernaut.

In a much anticipated move, Seattle-based Zillow today unveiled a new way for consumers to list and search for rental homes. Since its launch nearly four years ago, Zillow has primarily focused on helping buyers and sellers of homes determine how much they should pay and where they should live.

But with today's announcement, the company is broadening its focus and adding a new revenue model that could prove quite lucrative.

As part of the new service, the company has begun charging landlords $9.95 to have their rental properties appear at the top of search results on Zillow for 180 days. (Editor's note: The post has been updated with new information on the business model).

Homes for rent now appear on the Zillow map as purple house icons -- appearing along side red icons (homes for sale); yellow icons (recently sold homes); and blue icons (for sale by owner properties).

What will be interesting to watch is whether Zillow takes the paid listing model for rentals and applies it to the more lucrative for-sale market. Real estate agents could be interested in paying a little more to have their homes appear in the top of search results, or to add more photos, videos or other features in order to help sell a home.

Zillow has been juicing the revenue engines in recent months, expanding beyond the traditional advertising units that visitors see on the site. In fact, the company recently started charging lenders as part of its online marketplace for mortgages.

The new business models are already sparking some speculation that Zillow -- which has raised $87 million in venture capital -- could be positioning for an IPO in 2010.

Zillow's new service for rentals is just getting started. A search on Seattle rentals, for example, produced only three properties.

The service has some other unique features for those considering whether to buy, sell or rent. The company said it has built a tool which allows consumers to search homes by monthly payments, providing results both for rental properties and homes for sale.

With the new service, consumers can determine if they should rent or buy in a select neighborhood.

“In today’s volatile housing market, many would-be sellers are opting to rent for a few years and ride out the market, while many home shoppers are just trying to decide whether to buy or rent,” said Zillow Chief Operating Officer Spencer Rascoff in a release. “With the launch of rental listings and search, we are arming our more than 8 million monthly users with information, tools and options to make the right housing decisions for them today.”

Zillow.com is now one of the top online real estate destinations in the country, with Hitwise recently saying that it attracts more visitors than every site except Realtor.com. The company attracted on average 8.3 million unique visitors a month this year.

That compares to 2.8 million for Primedia's network of real estate sites -- including ApartmentGuide.com and Rentals.com.

UPDATE: A reader points out that Zillow also has begun charging real estate agents and others $9.95 to manually list their individual properties on the site. Here's what a spokeswoman had to say about the change.

"Charging for manual listings will help improve the consumer experience, because paying advertisers have more incentive to maintain accurate, updated information in their listings."

John Cook is co-founder of TechFlash. Follow on Twitter @johnhcook.