  We present a study of the effects of inelastic scattering on the transport
properties of various nanoscale devices, namely H$_2$ molecules sandwiched
between Pt contacts, and a spin-valve made by an organic molecule attached to
model half-metal ferromagnetic current/voltage probes. In both cases we use a
tight-binding Su-Schrieffer-Heeger Hamiltonian and the inelastic effects are
treated with a multi-channel method, including Pauli exclusion principle. In
the case of the H$_2$ molecule, we find that inelastic backscattering is
responsible for the drop of the differential conductance at biases larger than
the excitation energy of the lower of the molecular phonon modes. In the case
of the spin-valve, we investigate the different spin-currents and the
magnetoresistance as a function of the position of the Fermi level with respect
to the spin-polarized band edges. In general inelastic scattering reduces the
spin-polarization of the current and consequently the magnetoresistance.
