We demonstrate GaAs optomechanical crystals with large coupling rates (g(0)/2 pi approximate to 1.1MHz) through the photoelastic effect. We show a significant (approximate to 30%) orientation dependence of g0, observe 2.5 GHz regenerative oscillations, and explore excitation via piezoelectricallydriven surface-acoustic-waves. (C) 2014 Optical Society of America