  We present a new QCD sum rule with high sensitivity to the continuum regions
of charm and bottom quark pair production. Combining this sum rule with
existing ones yields very stable results for the MS-bar quark masses, m_c(m_c)
and m_b(m_b). We introduce a phenomenological parametrization of the continuum
interpolating smoothly between the pseudoscalar threshold and asymptotic quark
regions. Comparison of our approach with recent BES data allows for a robust
theoretical error estimate. The parametric uncertainty due to alpha_s is
reduced by performing a simultaneous fit to the most precise sum rules and
other high precision observables. This includes a new evaluation of the
lifetime of the tau lepton, tau_tau, serving as a strong constraint on alpha_s.
Our results are m_c(m_c) = 1.289 +0.040 -0.045 GeV, m_b(m_b) = 4.207 +0.030
-0.031 GeV (with a correlation of 29%), and alpha_s(M_Z) [tau_tau] = 0.1221
+0.0026 -0.0023.
