Ozone has a dipole moment of 0.53D. If you look at the Lewis structures, the central O has a positive charge and the terminal atoms share a negative charge. That's what comes of giving each atom a complete octet. Although there is no electronegativity difference between the atoms, the electron distribution is such that the centres of positive and negative charge do not coincide, so there is a dipole moment. This is generally the case for bent (C2v) molecules, or any where the symmetry does not compel a zero dipole moment.