  We study moduli spaces of (semi-)stable representations of one-point
extensions of quivers by rigid representations. This class of moduli spaces
unifies Grassmannians of subrepresentations of rigid representations and moduli
spaces of representations of generalized Kronecker quivers. With homological
methods, we find numerical criteria for non-emptiness and results on basic
geometric properties, construct generating semi-invariants, expand the Gel'fand
MacPherson correspondence, and derive a formula for the Poincare polynomial in
singular cohomology of these moduli spaces.
