ZillowOnline real estate company Zillow will join the wave of consumer Web companies filing for initial public offerings. The Seattle-based organization, which first made a name for itself by publishing price estimates for homes, just filed an S-1 outlining its plans for a $51.75 million IPO.

Zillow has been expected to go public for a while now, thanks in part to hints from the company’s executives. In September, VentureBeat’s Owen Thomas speculated about whether the appointment of Spencer Rascoff as chief executive suggested that the company was calling off the IPO (since Rascoff didn’t have experience running a public company), but Bloomberg reported in March that the company has chosen Citigroup to manage the offering — which turns out to have been true.

The offering is a bit smaller than some of the other noteworthy IPO filings from the past few months, including LinkedIn ($175 million), Pandora ($100 million), and HomeAway ($230 million). In fact, it’s even smaller than the $87 million in venture capital that Zillow has already raised.

The S-1 filing says that Zillow’s revenue is on the rise, having reached $30.5 million 2010, but the company still lost $6.8 million that year. (It mostly makes money from advertising.) The filing also says Zillow averaged 12.7 million unique visitors each month during the last quarter of 2010, up 66 percent from the year before.

Zillow rival Trulia has also stated its intentions to go public.