As the title of this thread is
Qabalah books, I thought I would add what I consider to be absolutely essential reading. These texts form, so to speak, the backbone of Kabbalistic tradition, which itself rests on the Old Testament.
- Sefer Yetzirah (also transliterated as Sepher Yezirah).
A. Kaplan's translation(s) of this book, and commentary, probably remains unsurpassed (published by Weiser, 1997). A very useful and different translation has also been done by Wescott (of the Golden Dawn), and another by I. Kalisch in 1877, still published by AMORC.
- Sefer Bahir (sometimes simply called 'The Bahir)'.
Again, A. Kaplan's translation and commentary stand, to my knowledge, unsurpassed.
- Sefer Zohar (again sometimes simply called 'The Zohar'.
Here G. Scholem's multi-volume work remains the standard. Scholem has also edited this into a very manageable 'little' extract of a mere 124 pages, published by Rider in 1977. I only have this edition, though I am aware that others exist.
Apart from these, a wide variety of Kabbalistic books are in existence, including some other highly worthwhile ones by, again, Gershom Scholem and Aryeh Kaplan, as well as Moshe Idel.
In my opinion, the three above mentioned texts, and the three above mentioned authors, can provide solid foundations for someone with the will to undertake the necessary studies.