Attention, all real estate junkies: something big just hit the market, and it's not your dream house. Today, Zillow  announced that it will acquire its competitor Trulia  in a $3.5 billion (yes, billion) stock deal. Expected to close this next year, the online real estate sites will continue to remain separate, but Trulia CEO Pete Flint will report to Zillow CEO Spencer Rascoff. This is good news, right? Yes, the companies hope that the acquisition will provide each brand with better opportunities for ad sales — the main source of revenue for both companies. But there's still room to grow. According to USA Today , the combined revenue of both companies still represents less than four percent of the nearly $12 billion that real estate professionals spend on marketing. Currently, Zillow shares are down more than three percent in early trading to $153.74, while Trulia stock is up more than 13 percent to $63.99 a share.