I think many, if not all of his ideas show up in all of his writings here and there, he is consistent that way :) But what still positively surprised my about "The Sane Society" was the last third, where he goes into (then) recent history, and quotes a lot of people I never heard of about the up and coming age of industrialization. Very good stuff, and all news to me.
At the risk of overdoing it (even more), one last quote I consider a true pearl because it sums up so much, from http://www.marxists.org/archive/fromm/works/1961/man/ :
The whole concept of alienation found its first expression in Western thought in the Old Testament concept of idolatry. The essence of what the prophets call "idolatry" is not that man worships many gods instead of only one. It is that the idols are the work of man's own hands -- they are things, and man bows down and worships things; worships that which he has created himself.
In doing so he transforms himself into a thing. He transfers to the things of his creation the attributes of his own life, and instead of experiencing himself as the creating person, he is in touch with himself only by the worship of the idol. He has become estranged from his own life forces, from the wealth of his own potentialties, and is in touch with himself only in the indirect way of submission to life frozen in the idols. The deadness and emptiness of the idol is expressed in the Old Testament: "Eyes they have and they do not see, ears they have and they do not hear," etc.
The more man transfers his own powers to the idols, the poorer he himself becomes, and the more dependent on the idols, so that they permit him to redeem a small part of what was originally his. The idols can be a godlike figure, the state, the church, a person, possessions. Idolatry changes its objects; it is by no means to be found only in those forms in which the idol has a socalled religious meaning.
Idolatry is always the worship of something into which man has put his own creative powers, and to which he now submits, instead of experiencing himself in his creative act.
Among the many forms of alienation, the most frequent one is alienation in language. If I express a feeling with a word, let us say, if I say "I love you," the word is meant to be an indication of the reality which exists within myself, the power of my loving. The word "love" is meant to be a symbol of the fact love, but as soon as it is spoken it tends to assume a life of its own, it becomes a reality. I am under the illusion that the saying of the word is the equivalent of the experience, and soon I say the word and feel nothing, except the thought of love which the word expresses.
The alienation of language shows the whole complexity of alienation. Language is one of the most precious human achievements; to avoid alienation by not speaking would be foolish -- yet one must be always aware of the danger of the spoken word, that it threatens to substitute itself for the living experience. The same holds true for all other achievements of man; ideas, art, any kind of man-made objects. They are man's creations; they are valuable aids for life, yet each one of them is also a trap, a temptation to confuse life with things, experience with artifacts, feeling with surrender and submission.
To me Erich Fromm's writings are like a holograms, they all seem to contain a rough version of the whole ^^