The Web services framework is enabling applications from different providers to be offered as services that can be used and composed in a loosely-coupled manner. Subsequently, the aggregation of services to form composite applications and maximize reuse is key. While choreography has received the most attention, services often need to be aggregated in a much less constrained manner. As a number of different mechanisms emerge to create these aggregations, their relation to each other and to prior work is useful when deciding how to create an aggregation, as well as in extending the models themselves and proposing new ones. In this paper, we discuss Web services aggregation by presenting a first-step classification based on the approaches taken by the different proposed aggregation techniques. Finally, a number of models are presented that are created from combinations of the above.