Recommended Apartment Searching Sites for the City

My wife and I will be searching for an apartment in Houston or outside the loop the next few months. What are some good sites and areas to search apartments in or around the city?

Also I'll be commuting to Katy and she will be commuting to the Med center. We're in Pearland right now but are looking for a change after growing up here. We both love the city but know there are cons to living in certain areas but we are open to suggestions. Thanks