We discuss associated neutralino production e^+ e^- --> \tilde{\chi}^0_1
\tilde{\chi}^0_2 with both beams polarized in the MSSM, NMSSM and an E_6 model.
It is shown that neutralinos with a large singlino component can be produced at
a high luminosity linear collider in a broad parameter range. Polarization
effects in the extended models are compared over the whole parameter space
where the lightest neutralino is mainly a singlino. We explain the complete
different behavior of these models in some parameter regions, which may help to
identify the respective supersymmetric model.Comment: 10 pages, LaTeX, 10 eps figures, contribution to the Proceedings of
the "2nd Joint ECFA/DESY Study on Physics and Detectors for a Linear
Electron-Positron Collider
