  Motivated by various spin-1/2 compounds like Cs$_2$CuCl$_4$ or
$\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, we derive a Raman-scattering operator
{\it \`a la} Shastry and Shraiman for various geometries. For T=0, the exact
spectra is computed by Lanczos algorithm for finite-size clusters. We perform a
systematic investigation as a function of $J_2/J_1$, the exchange constant
ratio: ranging from $J_2=0$, the well known square-lattice case, to $J_2/J_1=1$
the isotropic triangular lattice. We discuss the polarization dependence of the
spectra and show how it can be used to detect precursors of the instabilities
of the ground state against quantum fluctuations.
