The four measurements that must always be used are:
1.) The customer is satisfied
2.) The project is delivered within or under budget
3.) The project is completed on time
4.) The project's requirements have been met
Keep in mind the most important measure of project success is Customer Satisfaction. If you deliver a project on-time, within budget and it meets all requirements yet the customer is not satisfied, the project is a FAILURE!
Keep your customers (stakeholders/sponsor) informed throughout the project. Communicate to your customers using face-to-face conversations (yes, good project managers actually do this), status reports, e-mail, status meetings, voice mail, formal documentation, even sky writing if you have to. Your customers must be kept informed and remain engaged throughout the project. If you aren't hearing from them during your project, you aren't communicating with them. We all know that effective communications are two-way. If members of your project team choose not to communicate with you during your project look to have them removed from the team immediately.
In closing, maintaining a dialogue with your customers throughout your project helps you to address concerns and issues quickly. Combining effective communications and management of the project's triple constraints (Time, Cost Quality/Requirements) will help to ensure that your customers are satisfied with the end result of the project.