We present new high-quality light curves for the transiting planet XO-1b and TrES 2obtained in the SDSS z band using KeplerCam on the 1.2-m telescope at the Whipple Observatory on Mount Hopkins, Arizona. The z band was chosen to minimize the effects of limb darkening. We use the observations to update the radius and orbital inclination of the planets. We also present mass and radius determinations for some M dwarfs eclipsing F and G stars originally identified by the Vulcan, TrES, and HAT wide-angle surveys. These have light curves which are almost indistinguishable from transiting giant planets. In those cases where the rotation of the primary star has been synchronized with the orbital period we can use the observed broadening of the spectral lines to derive the radius and mass of the host star, and therefore the mass and radius of the unseen M dwarf.