Professional mashups that include complex choreographies, data mediation, and result publishing within Web pages are still affected by implementation and design practices that rely either on very simple models or on low-level scripting and programming skills of developers, thus hampering the use of mashups in business context as rapid solution to immediate problems. Indeed, industrialization of their development is still a hard objective to achieve. We propose a design methodology based on visual models to improve the quality and the productivity of service mashups and presentation of the results, thus increasing their acceptance as professional applications in the business scenario. Existing software engineering methods are combined together in an innovative mix, comprising standard business process modeling languages (namely, BPMN) to describe a high-level view of the mashup orchestration and on WebML (Web Modeling Language) to specify the detailed Web application model, including Web service interactions, hypertext navigation, event management, and rich user interfaces.