I'm very excited to write that I recently acquired a new book (actually a two-volume set) by Avraham Stahl:
מילון דביר דו-לשוני אטימולוגי לערבית מדוברת ולעברית
Bilingual Etymological Dictionary of Spoken Israeli Arabic and Hebrew
This really helps my library of etymological resources. The book has around 7000 entries for Arabic words, and etymological background for most of them. This helps understand the development of words in modern Hebrew (particulary slang) and to find Hebrew cognates for Arabic words that entered English.
Stahl is also the author of Motza HaMilim, which I often refer to. In general, I will refer simply to "Stahl", but when necessary, I will mention which book provides the information.