HDR photography is the new hotness in digital photography at the moment. While most people's introduction to HDR is with an unnatural, overproduced image done for artistic purposes, it is a very important technique for real estate photography.
HDR improves image quality by increasing the dynamic range of the photograph. Simply put, it uses the information from different exposure levels to produce a single image, where the final image has "better" exposure for each pixel than without the technique. An HDR photograph will have more shadow detail, highlights, and overall better exposure than a non-HDR photograph. You will be able to see through bright windows and capture better color information in outside shots.
Tasteful use of HDR techniques can produce lighting effects that normally require extensive and time-consuming lighting. It's also tricky to do, making it a great marketing tool to show the benefits of using a professional real estate photographer versus do-it-yourself shots by an agent.
The technique can be applied to stills as well as panos. In panos it can be especially useful since the lighting conditions can change dramatically as you shoot all of the stills that go into the panorama.
Nearly all professional image editing tools have some support for HDR at this point in time, including Photoshop, some stitchers like PTGui, and dedicated HDR tools like Photomatix. There are also open-source tools for doing HDR, the most popular being QTPFSGUI.
A related but different technique to HDR is called Exposure Fusion. Exposure fusion simply blends multiple exposures of the same shot to produce more even lighting. Exposure fusion is accomplished using a tool called enfuse and is supported by Photomatix, Bracketeer, and other tools.