  We identify SDSS011009.09+132616.1, SDSS030308.35+005444.1,
SDSS143547.87+373338.5 and SDSS154846.00+405728.8 as four eclipsing white dwarf
plus main sequence (WDMS) binaries from the Sloan Digital Sky Survey, and
report on follow-up observations of these systems. Orbital periods and
ephemerides have been established from multi-season photometry. SDSS1435+3733,
with Porb=3h has the shortest orbital period of all known eclipsing WDMS
binaries. Time-resolved spectroscopic observations have been obtained and the
radial velocities of the secondary stars in all four systems were measured. A
spectral decomposition/fitting technique was then employed to determine the
white dwarf effective temperatures and surface gravities, as well as the
spectral types of the companion stars. We used a light curve modeling code to
further constrain the masses and radii of the components in all systems. All
three DA white dwarfs have masses of Mwd~0.4-0.6Msun, in line with the
expectations from close binary evolution. The DC white dwarf in SDSS0303+0054
has a mass of Mwd>0.85Msun, making it unusually massive for a post-common
envelope system. Our new additions raise the number of known eclipsing WDMS
binaries to fourteen, and we find that the average white dwarf mass in this
sample is <Mwd>=0.57+/-0.16Msun, only slightly lower than the average mass of
single white dwarfs. The majority of all eclipsing WDMS binaries contain
low-mass (<0.6Msun) secondary stars, and will eventually provide valuable
observational input for the calibration of the mass-radius relations of
low-mass main sequence stars and of white dwarfs.
