Salvete collegae
Here is the list of modern authors I usually refer to for Roman history. Gibbons and Mommsen are standard starting points in the historiography of Rome. Still valid in much that they wrote. Taylor on party politics is still a standard, a bit dated though. Most of the rest challenge the conventional views with strong arguments to revise our perspectives of Roma antiqua. You will not find on my list any books by Michael Grant or other authors of "popular history." I am just not into light reading of the narrative type, but prefer the presentation of a good argument.
Beard, M., Crawford, M. (1985) Rome in the Late Republic Ithica.
Cornell, T. J. (1995) The Beginnings of Rome New York.
Crawford, M. (1978) The Roman Republic, Harvard.
Ferrill, A. (1986) The Fall of the Roman Empire: The Military Explanation, New York.
Gibbon, E. The Decline and Fall of the Roman Empire.
Grandazzi, A. Todd, J. M. (1997) The Foundations of Rome: Myth and History
Gruen, Erich S (1995). The Last Generation of the Roman Republic, California.
Holloway, R. R. (1994) The Archaeology of Early Rome and Latium, London.
Momigliano, A, di Donato, R. (1992) The Classical Foundation of Modern Historiography
Momigliano, A. (1989) Roma Arcaica, Florence.
Momigliano, A. (1961) Claudius, the Emperor and His Achievement, New York
Momigliano, A. (1966) Studies in Historiography, New York.
Momigliano, A. (1987) On Pagans, Jew, and Christians, Hanover, NH.
Mommsen, T. trans D. A. Saunders and J. H. Collins (1958) The History of Rome, Clinton, Ma.
Pallottino, M. (1991) History of Earliest Italy, Milan.
Pallottino, M. (1993) Origini e Storia Primitiva Roma, Milan.
Rawson, E. (1985) Intellectual Life in the Late Roman Republic, Baltimore
Salmon, E. T. (1967) Samnium and the Samnites, Cambridge.
Scullard, H. H. (1979) Roman Britain: Outpost of the Empire, London
Syme, R. (1980) Some Arval Brethren, Oxford.
Syme, Ronald (2002) The Roman Revolution Oxford.
Taylor, L. R. (1949) Party Politics in the Age of Caesar
Valete optime
Moravius Piscinus
Consul iterum