I delighted to find yesterday that the 91st edition of the Handbook of Chemistry and Physics is online (to subscribers). I think looking at the data is great anti-dote to the hubris of theorists, particularly reductionists. For example, how many of the listed properties (or even trends therein) can we accurately calculate, whether it is melting temperatures of simple solids or electron affinities of organic molecules?
The fact that spectroscopic properties of diatomic molecules are parametrised in terms of the Morse potential shows how good that empirical potential is!
Now the meaning of "handbook" becomes even stranger. Many editions ago the book ceased to be something you could hold in your hand! Now, in some sense it isn't even a book!