  In this letter, we propose three different strategies to extract the weak
mixing angle phi_s of the Bs system using penguin-mediated decays into vectors,
mainly Bs->K*K*, Bs->phi K* and Bs->phi phi. We also provide predictions for
the longitudinal branching ratio and CP-asymmetries of Bs->K*K* using a method
that combines QCD factorisation with flavour symmetries to relate this decay to
its Bd counterpart.
