Real-estate Web site http://Zillow.com became an instant hit by telling homeowners — and their nosy neighbors — how much their house may be worth.

Now, the Seattle-based company will help owners get the word out about how much they want in a sale.

Starting today, Zillow joins a growing list of Web sites that allow homeowners and real-estate agents to post virtual "For Sale" signs for free. The feature also plugs a hole on the site, which touts a database of more than 60 million U.S. residences but no information on what most viewers want to know: Is this home for sale?

The addition could pose yet another threat to the traditional system for buying and selling homes, analysts said.

"It's just one more chink in the armor of the established brokerage industry," said Steve Murray, an industry consultant based in Littleton, Colo. "It provides consumers with more choices."

Property listings are among the chief reasons consumers and advertisers seek out real-estate sites, and those with the biggest inventories of homes for sale get the most viewers. The No. 1 real-estate site is http://Realtor.com, which offers nothing but for-sale listings.