  We present detailed calculations of the neutralino-stop coannihilation
channels that have the largest impact on the relic neutralino density in the
constrained minimal supersymmetric extension of the Standard Model (CMSSM), in
which scalar masses m_0, gaugino masses m_1/2 and the trilinear soft
supersymmetry-breaking parameters A_0 are each assumed to be universal at some
input grand unification scale. The most important stop-stop* and stop-stop
annihilation channels are also calculated, as well as stop-slepton
coannihilation channels. We illustrate the importance of these new
coannihilation calculations when A_0 is relatively large. While they do not
increase the range of m_1/2 and hence neutralino mass allowed by cosmology,
these coannihilation channels do open up new `tails' of parameter space
extending to larger values of m_0.
