The Complete Tales and Poems of Edgar Allan Poe — The essential Poe collection: the stories, the poems, and the essays. Given the Deer Park Tavern's claimed connection to the man, it is the obvious reading companion for a visit to Newark.
A Delaware History by Harold Hancock — A solid one-volume account of Delaware from colonial times to the twentieth century. Puts Newark and the University of Delaware in their broader state context and is especially good on the colonial and Civil War periods.
College Towns: The Geography of Education by Blake Gumprecht — A thoughtful examination of how American college towns develop their character, with case studies from across the country. Newark fits the template well and reading this sheds light on what makes the town tick.
Piedmont Trails: Natural History of the Mid-Atlantic Foothills — A field guide to the geology, flora, and fauna of the Piedmont region that covers Delaware, Pennsylvania, and Maryland. Useful background for walking the trails at White Clay Creek State Park and understanding the Iron Hill geology.