We report on chemically prepared silver nanowires (diameters around 100 nm) sustaining surface plasmon modes with wavelengths shortened to about half the value of the exciting light. As we find by scattered light spectroscopy and near-field optical microscopy, the nonradiating character of these modes together with minimized damping due to the well developed wire crystal structure gives rise to large values of surface plasmon propagation length and nanowire end face reflectivity of about 10 microm and 25%, respectively. We demonstrate that these properties allow us to apply the nanowires as efficient surface plasmon Fabry-Perot resonators.