I am trying to become much better acquainted with the history of philosophy, and major perspectives from the presocratics and ancient Greeks to more modern perspectives (Kant, Schopenauer, Nietzsche, Bergson, etc.). So far I have read Durant's "The Story of Philosophy" and Russell's "The History of Western Philosophy". I found Durant to be wonderfully written but at times incomplete as to other major thinkers, while Russell feels a bit more biased while also omitting some major questions I would have wanted him to answer.
What other textbooks, or volumes are considered the best resources to become more knowledgeable about this fascinating area of study?
One of the best resources to learn about philosophy ist the Stanford Encyclopdia of Philosophy. The articles are usually of high quality, written by experts and citable in academia. It is of course an encyclopedia, so you would have to search for your interests and/or specific philosophers or subjects.
Check out Meditations, written by Roman Emperor Marcus Aurelius during the late 2nd century. It is a text on his brand of stoicism and an excellent insight into Roman philosophy during the height of the Empire.
It's a great read and it is remarkably relevant today. The whole thing is full of excellent quotes:
This world is mere change, and this life, opinion. (Fourth Book, III)
Marcus Aurelius was truly a philosopher ruler, one of the reasons he was my favorite Roman Emperor.