At 360 Integration we have a detailed model for web development which we follow for all of our projects. This approach ensures that the site is completed on time with no suprises. It also ensures that you know exactly what you'll receive when the project is complete.
Testing
Though we test what we write incrementally, we still like to set aside a portion of time prior to deployment for a complete test. Depending on the scale of the product this can incorporate a large number of people, from client and developer to a group of outside usability testers.