A particular higher-derivative extension of the Einstein-Hilbert action in
three spacetime dimensions is shown to be equivalent at the linearized level to
the (unitary) Pauli-Fierz action for a massive spin-2 field. A more general
model, which also includes `topologically-massive' gravity as a special case,
propagates the two spin 2 helicity states with different masses. We discuss the
extension to massive N-extended supergravity, and we present a
`cosmological' extension that admits an anti-de Sitter vacuum.Comment: Minor corrections plus a further correction to discussion of
supersymmetry in adS vacua, Version to be publishe