You would have to pay for what's called a flat fee listing service for your home to be on Trulia. You can easily post on Zillow, though.
We created UpNest (http://www.upnest.com) to help home sellers get the best value possible. All you have to do is submit a few details about your home, and we'll invite several top local agents to submit proposals to you. Since agents are competing to earn your listing, they bring out their best commission rates and value added services, saving you a lot of money. There's no risk to try us out at all, and it's completely free for you.