(FORTUNE Small Business Magazine) - The 6% real estate commission has been under assault awhile, but the hits just keep coming - and are getting more sophisticated. Three Internet upstarts are the latest to take a shot.

1. Redfin

Coverage: Seattle and San Francisco, and coming soon to Los Angeles and San Diego

What it does:

Superimposes for-sale information, as well as recent sale prices, on an aerial map. Launched in February, Redfin also acts as a buyer's agent and refunds two-thirds of the agent's commission--usually 2% of the total sales price--to the buyer. "We've had agents write in blogs about breaking our kneecaps," says CEO Glenn Kelman.

2. PropertyShark

Coverage: mainly New York City

What it does:

Publishes property record data in an online property report. Casual users can receive six reports a day for free; unlimited access costs $250 to $550 per year. Founder Matthew Haines says that when the site launched in January 2003, it "really agitated the brokers because they were used to having an information advantage."

3. Zillow.com

Coverage: National

What it does:

Aggregates information--such as aerial photos, assessed value, comparable recent sales, and lot size-on about 65 million of the country's 85 million single-family homes, with enough data to peg a value-a "Zestimate"-on more than 45 million of them. The site, which is run by the founders of Expedia (Research) and Hotwire.com, had nearly three million visitors during its three weeks live in February.

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