With the advance of the Cloud Computing paradigm, a single service offered by a cloud platform may not be enough to meet all the application requirements. To fulfill such requirements, it may be necessary, instead of a single service, a composition of services that aggregates services provided by different cloud platforms. In this perspective, this work presents Cloud Integrator, a middleware platform for composing services provided by different Cloud Computing platforms. Composition is performed by considering metadata about the services such as QoS, prices etc. By integrating the complementary paradigms of Service-Oriented Computing and Cloud Computing, Cloud Integrator enables the use of services provided by providers in a transparent way for the user, being necessary solutions for publishing, discovering, and composing these services. In terms of cloud infrastructure, Cloud Integrator lies in the PaaS layer, allowing HaaS, SaaS and DaaS resources to be available for the users so that they can build applications consisting of the composition of services provided by these platforms. In this paper, the application of Cloud Integrator is illustrated using a simple cloud-based e-commerce application.