We present results from 21 cm radio synthesis imaging of 28 spiral galaxies from the DiskMass Survey obtained with the VLA, WSRT, and GMRT facilities. We detail the observations and data reduction procedures and present a brief analysis of the radio data. We construct 21 cm continuum images, global Hi emission-line profiles, column-density maps, velocity fields, and position-velocity diagrams. From these we determine star formation rates (SFRs), Hi line widths, total Hi masses, rotation curves, and azimuthally-averaged radial Hi column-density profiles. All galaxies have an Hi disk that extends beyond the readily observable stellar disk, with an average ratio and scatter of RHI/R25 = 1.35 ± 0.22, and a majority of the galaxies appear to have a warped Hi disk. A tight correlation exists between total Hi mass and Hi diameter, with the largest disks having a slightly lower average column density. Galaxies with relatively large Hi disks tend to exhibit an enhanced stellar velocity dispersion at larger radii, suggesting the influence of the gas disk on the stellar dynamics in the outer regions of disk galaxies. We find a striking similarity among the radial Hi surface density profiles, where the average, normalized radial profile of the late-type spirals is described surprisingly well with a Gaussian profile. These results can be used to estimate Hi surface density profiles in galaxies that only have a total Hi flux measurement. We compare our 21 cm radio continuum luminosities with 60 μm luminosities from IRAS observations for a subsample of 15 galaxies and find that these follow a tight radio-infrared relation, with a hint of a deviation from this relation at low luminosities. We also find a strong correlation between the average SFR surface density and the K-band surface brightness of the stellar disk.