  We discuss how dileptons, open charm and charmonia may be utilized in
heavy-ion collisions to extract information specific to hot and dense matter at
finite quark chemical potential, $\mu_q$. For each observable we briefly
discuss underlying theoretical frameworks and the current status in
interpreting available heavy-ion data at SPS and RHIC energies. Low-mass
dileptons are particularly sensitive to baryonic medium effects in spectral
modifications of the $\rho$ meson, and may serve as an accurate measure of the
fireball lifetime. In the open-charm sector, observable signals may be
generated by a ``critical'' enhancement of scattering rates via $t$-channel
exchange of a soft $\sigma$ mode. For charmonia, finite-$T$ potential models
could be used to extrapolate color-screening effects to finite $\mu_q$ to
facilitate a quantitative evaluation of dissociation rates in the medium.
