What is the Bekenstein-Hawking entropy? what is "quasinormal mode"? $A/4$?
The Beckenstein-Hawking entropy essentially says that the entropy of a black hole is proportional to its horizon area (the A in A/4; note that is in natural units -- there is a G, hbar, and k floating in it). This was recently generalized by Bousso to become the holographic principle, which states that the number of degrees of freedom (information content) in a volume of space is also proportional to the surface area of a bounding "light sheet". The holographic principle shows promising links between relativity and field theory, e.g. the AdS/CFT correspondence.
The quasinormal mode has to do with resonance modes of a black hole, if I recall correctly. Dryer has derived an interesting result for this, which involves a factor of ln(3). I can't remember specifics (I saw him speak about it at a conference last summer), but if you look up his other papers on arxiv, you'll find the appropriate references.