With this being a potentially subjective question I know I'm threading on thin ice, but this is an actual "physics" problem I face from time to time:
The situation is this: I hear about some phenomenon. For the sake of definiteness, let's say it is the Jahn-Teller-Theorem. I'd then like to find a good source that has a graduate level introduction to this phenomenon. The problem is that all Google turns up is either a very simplified explanation of the thing at hand (think Wikipedia), or a research level text that assumes its readers already have a perfect understanding of what the thing is. And original papers often do not provide such a clear answer (Legend has it that Born and Oppenheimer's paper on the adiabatic approximation is quite inaccessible and the relevant thing, the BO-Expansion, appears hidden somewhere in the appendix...).
I believe that I am not alone with this problem and I wonder if there is a straightforward approach to finding good introductory (but NOT superficial) texts on a given phenomenon.