Yes you can post your home For Sale By Owner on Zillow, Trulia FOR FREE!! You should also post it on other websites. Zillow and Trulia are the same company (Zillow Group). You need to start with Zillow, then it will sync to Trulia within 24 - 36 hours. You should receive a confirmation email.
WARNING: You need to know that realtors pay monthly advertising fees to Zillow, Trulia and other websites. Their names, pictures and contact information WILL APPEAR on all For Sale By Owner listings. You cannot remove them. The issue is Zillow and Trulia have a default checkmark next to one of the agents on your listing. This is done for the buyer's convenience. All the buyer has to do is fill out the Contact Form and submit it. The lead will go to the agent - not you, the owner. One method around this is to include a sentence in your description that says: "PLEASE CONTACT OWNER AT _____".
You also need to know that ALL realtors scan For Sale By Owner listings and are trained to call you. Whether or not you want a realtor, the fact that your home is for sale means you will receive phone calls from realtors. Realtors are trained to tell you that you don't know what you're doing and you need to list your home with a broker.
A hybrid method that will solve your issues is Google "Flat Fee Broker". There are several websites that do this. The process is it allows sellers to pay a small fee to have their home listed for sale in their local MLS system. Sellers are required to pay a buyers broker a commission (about 3% - it's negotiable). The HUGE benefit to sellers is you save the other 3% by not having a full service broker. As a seller, you will be in control of marketing, deadlines, contract, negotiations, disclosures, etc. Even if you pay for a real estate attorney and title company, it's still much cheaper than paying 6% + to a real estate brokerage.... more