Almost all real estate websites I have read are missing the essential information about a lease from their search filters. The core info is whether the property is available from a certain date to a certain date, whether the minimum and maximum lease lengths allow a tenancy for the specified term, what is the monthly rent for that term. Some websites specify that information in the description of the property, but do not allow searches based on it. On some websites, the rent doubles when the term is halved, which would be good to know from the start instead of after clicking on a search result.
If the property is only rented to a specific class people, e.g. requires a number of years of good rental history, a certain income level, etc, then it would be good to know this at the start of the search, instead of during the application process.
Almost useless info like hardwood floors, granite countertops, historic building, etc should be removed or relegated to the bottom of the page.
In general, any search website should allow the user to remove specific results (that the user has deemed irrelevant) from future searches, like Craigslist does. Being able to save the search like in Craigslist is also a useful feature.