In magnetic ultrathin films and dots, competing exchange, anisotropy and dipolar couplings lead to a large variety of magnetic structures. These structures are obtained by means of the Monte Carlo simulations. Three classes of magnetic structures are obtained according to anisotropy-to-dipolar energy ratio: Ising striped structures, XY-spin structures with vortices, and twisted spin phases at the spin reorientation transition. Domain wall nucleation and motion at the coercive field are also accessible.