  We present the results of a variational Monte Carlo calculation of the
exchange-correlation energy for a spin-polarized two-dimensional electron gas
in a perpendicular magnetic field. These energies are a necessary input to the
recently developed current-density functional theory. Landau-level mixing is
included in a variational manner, which gives the energy at finite density at
finite field, in contrast to previous approaches. Results are presented for the
exchange-correlation energy and excited-state gap at $\nu =$ 1/7, 1/5, 1/3, 1,
and 2. We parameterize the results as a function of $r_s$ and $\nu$ in a form
convenient for current-density functional calculations.
