The quark top stands out as the heaviest elementary particle known to date. Because its mass is of order of the electroweak symmetry breaking (EWSB)energy scale, this article is expected to play an essential role in the mechanism of EWSB. In particular, since the top quark lives very shortly and almost all the time decays into a b quark and a W boson, as predicted by the standard model (SM), new physics effects are likely to be more evident in those top quark processes that are forbidden or strongly suppressed in th SM. We show that this is in fact the case in decays induced by flavor changing neutral couplings (FCNC) and in the anomalous ttg coupling for several extensions of the SM: THDM, SUSY, Left-Right symmetric, TC2, 331, models with extra quarks or with a single extra dimension, and even for the new idea of unparticle physics.