Dozens of ultracool stars and brown dwarfs have been identified as candidate binary systems on the basis of peculiarities in their infrared spectra and/or colors. This detection method permits the discovery of short-period systems straddling the hydrogen burning mass limit, including P < 1 year binaries amenable to orbit measurement through radial velocity and astrometric monitoring. We report the discovery of several new radial velocity variables among sources observed with Keck/NIRSPEC. Using a forward-modeling approach, we are able to obtain velocities with < 0.5 km/s precision for M, L and T dwarfs, as well as rotational velocities and estimates of effective temperature and surface gravity. We report a complete radial velocity orbit for the L4+T5 binary SDSS J0805+4812AB, which has a period of 2.0 yr, semi-major axis of 0.74 AU, eccentricity of 0.46, and substellar component masses, with the primary near the lithium-burning mass limit. We also report the discovery of the first T dwarf radial velocity variable. We highlight several sources with long-term variations which may be resolvable with follow-up high-resolution imaging, and examine the distribution of rotational velocities in our broader sample.