  The one-orbital model for manganites with cooperative phonons and
superexchange coupling $J_{\rm AF}$ has been investigated via large-scale Monte
Carlo (MC) simulations. Results for two-orbitals are also briefly discussed.
Focusing on electronic density $n$=0.75, a regime of competition between
ferromagnetic (FM) metallic and charge-ordered (CO) insulating states was
identified. In the vicinity of the associated bicritical point, colossal
magnetoresistance (CMR) effects were observed. The CMR is associated with the
development of short-distance correlations among polarons, above the spin
ordering temperatures, resembling the charge arrangement of the low-temperature
CO state.
