Earl, Donald. The political thought of Sallust
Kapust, Daniel J. Republicanism, rhetoric, and Roman political thought: Sallust, Livy, and Tacitus
Leeman, A. D. A systematical bibliography of Sallust
Ring, Abram. Oxford Bibliography on Sallust
Syme, R. Sallust
Wilkins, Ann Thomas. Villian or Hero: Sallust's portrayal of Catiline
A Good Place to Start:
Oxford Bibliography on Velleius Paterculus by Eleanor Cowan, 2014
Velleius Paterculus in The Oxford Companion to Classical Civilization. 2014.
Other Sources:
Cogitore, I. "Portraits in the works of Velleius Paterculus." Latomus 68, no. 1 (2009): 51-72.
Connal, Robert T. "Velleius Paterculus: The Soldier and the Senator." Classical World 107, no. 1 (2013): 49-62.
Cowan, Eleanor. "Contesting Clementia: the Rhetoric of Severitas in Tiberian Rome before and after the Trial of Clutorius Priscus." JRS 106 (2016): 77-101.
Dawson, Christopher. "The Princeps Optimus: Towards a New Reading of Velleius Paterculus' History." Master's Thesis, 2008.
Kramer, Emil Augustine. "Imaging empire: Aspects of Velleius Paterculus' historiography." Dissertation, 1999.
Kuntze, Claudia. 1985. Zur Darstellung des Kaisers Tiberius und seiner Zeit bei Velleius Paterculus. Frankfurt am Main: P. Lang.
Ramage, Edwin S. "Velleius Paterculus 2.126.2-3 and the Panegyric Tradition." Classical Antiquity 1, no. 2 (1982): 266.
Saddington, D. B. "An Augustan Officer on the Roman Army: Militaria in Velleius Paterculus and Some Inscriptions." Bulletin of the Institute of Classical Studies, 46, S81 (2003): 19-29.
Starr, Raymond James. "Velleius Paterculus: A Literary Introduction." Dissertation, 1978.