Despite their dominance of high-end computing (HEC) through the 1980’s, vector systems have been gradually replaced by microprocessor-based systems. However, while peak performance of microprocessors has grown exponentially, the gradual slide in sustained performance delivered to scientific applications has become a growing concern among HEC users. Recently, the Earth Simulator and Cray X1/X1E parallel vector processor systems have spawned renewed interest in vector technology for scientific applications. In this work, we compare the performance of two Lattice-Boltzmann applications and the Cactus astrophysics package on vector based systems including the Cray X1/X1E, Earth Simulator, and NEC SX-8, with commodity-based processor clusters including the IBM SP Power3, IBM Power5, Intel Itanium2, and AMD Opteron processors. We examine these important scientific applications to quantify the effective performance and investigate if efficiency benefits are applicable to a broader array of numerical methods.