We report the growth and characterization of ultra-smooth, highly ordered, strained La2/3Ca1/3MnO3±d thin films (approximately 600 Å in thickness). The thin films were deposited by ozone-assisted, block-by-block, molecular beam epitaxy on SrTiO3 (001) substrates without any post-deposition annealing. Scanning tunneling microscopy images showed oriented, unit-cell-high terraces characteristic of a step-flow growth mechanism. The root-mean-square roughness of the surface of an imaged film was determined to be 2 Å. This same film showed negative magnetoresistance values, [R(H=0)-R(Happlied)]/R(H=0), at 150 K of 93% and 5% in applied magnetic fields of 5.12 and 4×10-2 T, respectively.