What Tc Tells
  Superconductivity has continued to be a fascinating phenomenon ever since its discovery in 1911. The magnitude of the transition temperature, Tc, provides valuable insight into the underlying physics. Here we provide select examples of the extensive research that has been done towards understanding Tc, and some cases where further investigation is called for. We believe that searching for new and enhanced Tc's remains a fertile frontier. 
Theodore H. Geballe, Robert H. Hammond, Phillip M. Wu
cond-mat.supr-con