  Coannihilation effects in neutralino relic density calculations are examined
for a full range of supersymmetry parameters including large \tan\beta and
large A_0 for stau, chargino, stop and sbottom coannihilation with the
neutralino. Supergravity models possessing grand unification with universal
soft breaking (mSUGRA), models with nonuniversal soft breaking in the Higgs and
third generation sparticles, and D-brane models with nonuniversal gaugino
masses were analysed. Unlike low \tan\beta where m_0 is generally small, stau
coannihilation corridors with high \tan\beta are highly sensitive to A_0, and
large A_0 allows m_0 to become as large as 1TeV. Nonuniversal soft breaking
models at high \tan\beta also allow the opening of a new annihilation channel
through the s-channel Z pole with acceptable relic density, allowing a new wide
band in the m_0-m_{1/2} plane with m_{1/2} >~ 400 GeV and $m_0$ rising to 1
TeV. The D-brane models considered possess stau coannihilations regions similar
to mSUGRA, as well as small regions of chargino coannihilation.
Neutralino-proton cross sections are analysed for all models and it is found
that future detectors for halo wimps will be able to scan essentially the full
parameter space with m_{1/2} < 1 TeV except for a region with \mu < 0 where
accidental cancellations occur when 5 ~<\tan\beta ~< 30. Analytic explanations
of much of the above phenomena are given. The above analyses include current
LEP bounds on the Higgs mass, large \tan\beta NLO correction to the b \to s
\gamma decay, and large \tan\beta SUSY corrections to the b and \tau masses.
