  High-accuracy binary black hole simulations are presented for black holes
with spins anti-aligned with the orbital angular momentum. The particular case
studied represents an equal-mass binary with spins of equal magnitude
S/m^2=0.43757 \pm 0.00001. The system has initial orbital eccentricity ~4e-5,
and is evolved through 10.6 orbits plus merger and ringdown. The remnant mass
and spin are M_f=(0.961109 \pm 0.000003)M and S_f/M_f^2=0.54781 \pm 0.00001,
respectively, where M is the mass during early inspiral. The gravitational
waveforms have accumulated numerical phase errors of <~ 0.1 radians without any
time or phase shifts, and <~ 0.01 radians when the waveforms are aligned with
suitable time and phase shifts. The waveform is extrapolated to infinity using
a procedure accurate to <~ 0.01 radians in phase, and the extrapolated waveform
differs by up to 0.13 radians in phase and about one percent in amplitude from
the waveform extracted at finite radius r=350M. The simulations employ
different choices for the constraint damping parameters in the wave zone; this
greatly reduces the effects of junk radiation, allowing the extraction of a
clean gravitational wave signal even very early in the simulation.
