Seth, God of Confusion Book
by Herman te Velde.
Te Velde looks at Seth's origins and the ever-puzzling question of what animal represents him before examining his major roles in detail: as the enemy and friend of Horus, the murderer of Osiris, the repeller of Apophis when sailing in Ra's barque, and as the god of foreigners. In doing so, he points out that Seth was not the simple villain that pop culture tends to see him as, though the overall picture he gives is still rather skewed to the negative. He doesn't devote much space to how Seth was worshipped, but he does refer to some of the developments in Seth's cult over time.
The book, originally published in 1967, is an early example of the Egyptological trend toward reading religion and myth as complex metaphors, as opposed to the older approach that often explained myths as the product of political history. (In fact, the book shows something of an argument between te Velde and J. Gwyn Griffiths, whose earlier book The Conflict of Horus and Seth is largely shaped by the older school of thought.) Te Velde's analysis of the symbolism in myth helps make sense of some of the bizarre mythic episodes about Seth, particularly in the conflict with Horus, although a couple of his interpretations look a bit far-fetched to me.
The major problem with the book, which I've seen many times in books on ancient Egyptian religion, is that it doesn't cover the periods after the New Kingdom very extensively. In this case there's some justification for that, because those were the periods when Seth was increasingly demonized and ceased to be worshipped. Or, at least, that's what was thought when te Velde was writing. Evidence discovered in recent decades, particularly from the Egyptian oases, now proves that his worship lasted into the Roman period, at least in some places. I don't think there's any extensive coverage of that subject yet, though a lot of the evidence can be found in the works of Olaf Kaper. Seth: A Misrepresented God in the Ancient Egyptian Pantheon? attempts a more up-to-date look at Seth's significance to the Egyptians, but it works better as a chronological listing of major evidence than an improvement upon te Velde's analysis.