  We consider the medium- and long-baseline oscillation physics capabilities of
intense muon-neutrino and muon-antineutrino beams produced using future
upgraded megawatt-scale high-energy proton beams. In particular we consider the
potential of these conventional neutrino ``superbeams'' for observing
\nu_\mu\to\nu_e oscillations, determining the hierarchy of neutrino mass
eigenstates, and measuring CP-violation in the lepton sector. The physics
capabilities of superbeams are explored as a function of the beam energy,
baseline, and the detector parameters. The trade-offs between very large
detectors with poor background rejection and smaller detectors with excellent
background rejection are illustrated. We find that it may be possible to
observe \nu_\mu\to\nu_e oscillations with a superbeam provided that the
amplitude parameter \sin^2 2\theta_{13} is larger than a few \times 10^{-3}. If
\sin^2 2\theta_{13} is of order 10^{-2} or larger, then the neutrino mass
hierarchy can be determined in long-baseline experiments, and if in addition
the large mixing angle MSW solution describes the solar neutrino deficit then
there is a small region of parameter space within which maximal CP-violation in
the lepton sector would be observable in a low-energy medium-baseline
experiment. We explicitly consider massive water Cherenkov and liquid argon
detectors at superbeams with neutrino energies ranging from 1 GeV to 15 GeV,
and baselines from 295 km to 9300 km. Finally, we compare the oscillation
physics prospects at superbeams with the corresponding prospects at neutrino
factories. The sensitivity at a neutrino factory to CP violation and the
neutrino mass hierarchy extends to values of the amplitude parameter \sin^2
2\theta_{13} that are one to two orders of magnitude lower than at a superbeam.
