The Greek Magical Papyri in Translation, by Betz: Certainly the most important, if not exactly the most convenient, source for ancient Hermetic practices.
Be aware that not all sheets survived entirely intact, necessitating a good deal of work to make these spells actually complete, let alone workable in a modern context. For the most part, it can be done though, and there is much of great value in here.
Also called the Papyri Graecae Magicae, PGM for short.
Hermetic Magic: The Postmodern Magical Papyrus of Abaris, by Flowers: This features a short introduction to Hermetic thought, along with a selection of modernized, complete spells sourced from the PGM, Very helpful, especially to the beginner. If you're just starting out or just want to get a single book to see what Hermetic Thought and Magic is about, this is what you want.
The Book of Abrasax, by Cecchetelli: Another collection of modernized spells, but without an introduction to the philosophy this time. More of a work for people already familiar with the ideas of Hermeticism. Nonetheless, a very helpful volume with a wide variety of usefull rituals
The Complete Magician's Tables, by Skinner: A reference book containing a variety of tables on the correspondences of various things in various traditions. Highly useful when personalizing rituals, or just attempting to understand them.