  We use Cosmic Microwave Background data from the WMAP, SPT, BICEP, and QUaD
experiments to obtain constraints on the dark matter particle mass $m_\chi$,
and show that the combined data requires $m_\chi > 7.6$ GeV at the 95%
confidence level for the $\chi \chi \rightarrow b \bar b$ channel assuming
$s-$wave annihilation and a thermal cross section $<\sigma_{\rm a} v> = 3
\times 10^{-26}$ cm$^3/$s. We examine whether the bound on $m_\chi$ is
sensitive to $\sigma_8$ measurements made by galaxy cluster observations. The
large uncertainty in $\sigma_8$ and the degeneracy with $\Omega_{\rm m}$ allow
only small improvements in the dark matter mass bound. Increasing the number of
effective neutrino-like degrees of freedom to $N_{\rm eff} = 3.85$ improves the
mass bound to $m_\chi > 8.6$ GeV at 95% confidence, for the $\chi \chi
\rightarrow b \bar b$ channel. We also study models in which dark matter halos
at $z<60$ reionize the Universe. We compute the Ostriker-Vishniac power
resulting from partial reionization at intermediate redshifts $10<z<60$, but
find the effect to be small. We discuss the importance of the large angle
polarization as a complementary probe of dark matter annihilation. By
performing Monte Carlo simulations, we show that future experiments that
measure the $EE$ power spectrum from $20 < l < 50$ can exclude $m_\chi \sim$ 10
GeV at the 2 (3) $\sigma$ level provided the error bars are smaller than 4 (3)
$\times$ cosmic variance. We show that the Planck experiment will significantly
improve our knowledge of dark matter properties.
