  We report on the long-term monitoring of three anomalous X-ray pulsars using
the Rossi X-ray Timing Explorer (RXTE). We present a phase-coherent timing
ephemeris for 4U 0142+61, and show that it has rotated with high stability over
4.4 yr, with RMS phase deviations of 7% of the pulse period from a simple fit
including only $\nu$ and $\dot{\nu}$. We report on the continued timing
stability of 1E 2259.1+586, for which phase coherence has now been maintained
over 4.5 yr, as well as on the detection of a significant $\ddot{\nu}$ in 1.4
yr of monitoring of RXS J170849.0-400910, consistent with recovery following a
glitch. We note a correlation in which timing stability in AXPs decreases with
increasing $\dot{\nu}$. The timing stability of soft gamma repeaters in
quiescence is consistent with this trend, given their large spin-down rates.
This trend is similar to one seen in radio pulsars, suggesting a connection
between the three populations. We find no large variability in pulse morphology
as a function of time. We present high signal-to-noise ratio average pulse
profiles for each AXP, and consider them as a function of energy. We find a
variety of different behaviors, and consider possible trends in the data. We
also find no large variations in pulsed flux, and set 1 $\sigma$ upper limits
of ~20-30% of the mean. Assuming a constant pulsed fraction, either more than
one of the AXPs are coincidentally in a much more quiescent state during our
RXTE monitoring than in the past, or past claims of large flux variations are
incorrect.
