You can list a home with one photo for free. If you want it to be a "featured" listing, which more photos and get more search hits, you can pay a fee of $39 a month.

If you click on "My Trulia" and select "My profile", there is a section called "my listings". There, you'll find a place where you can add a listing. It takes a couple days for the home to become active in the site. It seems like I posted my ad on a sunday morning, and it wasn't "live" and viewable to others until Tuesday. You then have to acknowledge the home is still active every couple of weeks so that search only has homes that are still available.

Hi Bart,
You need to contact Trulia directly but I think is free,
You can use also http://www.findurhouse.com it is for free also