I would check out "So You Want to be a Wizard" by Diane Duane, along with the sequels (Deep Wizardry, High Wizardry, etc.) The books are about wizards in the modern world who secretly defend against the forces of entropy, having fantastic adventures (sometimes in alternate primes, sometimes in strange settings in our own universe) along the way.
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Finally, for classic tales of wizardry, I would start with Ursula K. LeGuin's Wizard of Earthsea trilogy (A Wizard of Earthsea, Tombs of Atuan, the Farthest Shore, later followed by Tehanu.) A Wizard of Earthsea in particular is terrific.