According to the 2012 NAR (National Association of Realtors) profile of Home Buyers and Sellers, most buyers look to the local Multiple Listing Service website to view local listings prior to purchase. Next, they look at Realtor.com, the gorilla website in America, followed closely by agent's websites.

I just revamped my agent website at www.icrealestate.com with a great search feature making it easy to sort, view and print listings for sale or lease. I also put in links to sites I use in my daily real estate practice like traffic maps and the Johnson County GIS site. Go have a look, or I'll highlight this new website in a future post.
The NAR study puts company websites (pitty!) and other websites like Trulia last at 13% each. It was surprising that mobile and tablet apps were at 39%! I use the one for Realtor.com on my iPad for showing as it uses geocoding as a sort feature and I can find the homes closest to me.