I was pleasantly surprised by William Walker Atkinson's “The Secret Doctrine of the Rosicrucians”. Not because I agree with it (in fact, I disagree with large chunks of this material, including the Rosicrucian label), but because the work is written in an accessible style.
Published under the nom-de-plum Magus Incognito, Atkinson's book is an excellent introduction to a broadly Theosophical worldview. In fact, the very title of his book is an allusion to Madame Blavatsky's “The Secret Doctrine”. Dion Fortune's “The Cosmic Doctrine” seems to cover much the same ground (I think – it was frankly incomprehensible). Thus, Atkinson is good for those who stumbled rather badly when trying to digest Blavatsky's and Fortune's respective tomes. It's less clear whether the work can function as an intro to the Steiner-Heindel end of early 20th century occultism. Probably not, due to the often peculiar speculations of Anthroposophy, and also its “Christian” angle.
Another useful text from the same author (plus some collaborators) is “The Kybalion”, which I have reviewed elsewhere. I will give this work five stars, since it clarified much of my agreements or disagreements with this particular type of esotericism, which is still quite popular.