In this paper, we propose a simple but flexible virtual machine consolidation method for power saving. This method is specifically designed for datacenters where heterogeneous high-density blade servers host dozens or even hundreds of virtual machines. This method utilizes an extended First-Fit Decreasing (FFD) algorithm. It selects a migration destination server on the basis of server rank. The rank represents server selection priority and is uniquely assigned to each physical server. Our simulation results show that this method reduces power consumption by 34.5% under a typical workload and 33.8% under a random workload.