The Kybalion: Centenary Edition

If you can get beyond the silly ostentatious writing and Victorian-era science worship, it is a decent enough introduction to a few key Hermetic principles. However, for such a short book, it is incredibly repetitive. As must be explained, it is not The Kybalion itself, but is a commentary on The Kybalion (which most likely doesn't even exist); written not by three sages, but by one guy, William Walker Atkinson, and is largely comprised of his own ideas informed by the occultism of his day. I hesitate to recommend it at all as an introduction to Hermeticism, but it does organize and explain many principles more inappropriately than incorrectly and is, all said, pretty short.

If you are an educated reader who is ready to jump into the subject with both feet, I would skip this and head directly to something like a translation of The Corpus Hermeticum. If you are just vaguely curious as to what it's all about, this will likely suffice. But, be prepared to be annoyed by it's style if you have little patience for pompous gasbaggery.