Dark Energy Beyond the Standard Cosmological Model

We consider some models of dark energy based on perfect fluids, tachyons and phantom scalar fields. It is shown that the cosmological perturbations in the generalized Chaplygin gas model, where the pressure is inversely proportional to the power of the energy density which is greater than 3 are compatible with observations. The tachyon model, implying as a possible outcome of the cosmological evolution en encounter with the big brake cosmological singularity is compared with supernovae data and some characteristics of such evolutions are numerically estimated. Finally we consider a cosmological model with two scalar fields (one of which is effectively phantom), based on PT symmetry.