The field of user experience, is blessed (or cursed) with a very wide range of research methods, ranging from tried-and-true methods such as lab-based usability studies to those that have been more recently developed, such as desirability studies (to measure aesthetic appeal).
You can't use the full set of methods on every project, but most design teams benefit from combining insights from multiple research methods. The key question is what to do when. To better understand when to use which method, it is helpful to realize that they differ along 3 dimensions:
Attitudinal vs. Behavioral
Qualitative vs. Quantitative
Context of Website or Product Use The following chart illustrates where several popular methods appear along these dimensions:
More details...click here http://www.useit.com/alertbox/user-research-methods.html