  We present photometric and morphological analyses of nuclear star clusters
(NSCs) -- very dense, massive star clusters present in the central regions of
most galaxies -- in a sample of 33 massive disk galaxies within 20 Mpc, part of
the "Composite Bulges Survey." We use data from the Hubble Space Telescope
including optical (F475W and F814W) and near-IR (F160W) images from the Wide
Field Camera 3. We fit the images in 2D to take into account the full
complexity of the inner regions of these galaxies (including the contributions
of nuclear disks and bars), isolating the nuclear star cluster and bulge
components. We derive NSC radii and magnitudes in all 3 bands, which we then
use to estimate NSC masses. Our sample significantly expands the sample of
massive late-type galaxies with measured NSC properties. We clearly identify
nuclear star clusters in nearly 80% of our galaxies, putting a lower limit on
the nucleation fraction in these galaxies that is higher than previous
estimates. We find that the NSCs in our massive disk galaxies are consistent
with previous NSC mass-NSC radius and Galaxy Mass-NSC Mass relations. However,
we also find a large spread in NSC masses, with a handful of galaxies hosting
very low-mass, compact clusters. Our NSCs are aligned in PA with their host
galaxy disks but are less flattened. They show no correlations with bar or
bulge properties. Finally, we find the ratio of NSC to BH mass in our massive
disk galaxy sample spans a factor of $\sim$300.
