Web services provide the possibility of dynamically integrating distributed service components scattered over the Internet to fulfill sophisticated business demands. The effectiveness of service integration depends critically on the selection of best-fit service components. In this paper, we first review several research streams related to server selection. We then propose a framework of dynamic service discovery, termed Network Mapping Services (NMS), which combines prior efforts on network-aware applications and server selection into a coherent structure. As successful implementation of NMS requires the collaboration among all participating service providers, we also discuss several incentive schemes and compare their effectiveness in supporting collaboration.