  In this talk we present applications of the AdS/CFT correspondence to
strongly coupled systems at finite temperature and particle density. The model
we investigate contains adjoint matter described by the gauge multiplet of N=4,
as well as fundamental matter given by the hypermultiplet of N=2 Super
Yang-Mills theory. In some aspects these systems can be thought of as models
for the quark-gluon plasma.
  In the first part we review some properties of meson spectra obtained from
these holographic models. We discuss the implications of finite temperature and
particle density in these string-theory motivated setups. In particular, we
find a broadening of the vector meson peaks in the relevant spectral function
at finite density. However, we do not observe a movement of the resonances to
lower frequencies.
  Moreover, we analyze the effects of strong coupling on heavy meson diffusion
in medium. To do so, we make use of an effective model with dipole interaction,
which is valid for heavy quarks at arbitrary coupling strength. We calculate
the momentum broadening -- normalized to the in-medium mass shift -- and
compare the large 't Hooft coupling AdS/CFT result with a perturbative result
for weak coupling. We find that the momentum broadening is reduced at large 't
Hooft coupling, leading to increased relaxation time.
