  We study spectral properties of ergodic random Schr\"odinger operators on
$L^2 (\RR^d)$. The density of states is shown to exist for a certain class of
alloy type potentials with single site potentials of changing sign. The Wegner
estimate we prove implies Anderson localization under certain additional
assumptions. For some examples we discuss briefly some properties of the common
and conditional densities of the random coupling constants used in the proof of
the Wegner estimate.
