Some recent editions and translations of the Latin text.
Dass, Nirmal. 2011. The Deeds of the Franks and other Jerusalem-bound Pilgrims. Lanham, Md.: Rowman & Littlefield Publishers. [English only, with helpful notes.]
Hill, Rosalind. 1962. The Deeds of the Franks and the other Pilgrims to Jerusalem. London, New York: Thomas Nelson. [Latin text with English translation.] The Oxford University Press edition (1967, reprinted 1972, 1979) is available at Internet Archive.
Russo, Luigi. 2003. Le Gesta dei Franchi e degli altri Pellegrini Gerosolimitani. Alexandria: Edizioni dell'Orso. [Latin text with Italian translation and detailed notes.]
On the Gesta Francorum
France, John. 1998. “The Use of the Anonymous Gesta Francorum in the Early Twelfth-Century Sources for the First Crusade.” In From Clermont to Jerusalem: The Crusades and Crusader Societies, 1095–1500: Selected proceedings of the International Medieval Congress, University of Leeds, 10–13 July 1995, International Medieval Research 3, edited by Alan V. Murray, 29–42. Turnhout: Brepols.
Gavignan, John Joseph. 1943. “The Syntax of the Gesta Francorum.” Language 19 (3): 10–102. [A detailed study of the Latin of the Gesta Francorum and its differences from Classical Latin; its references are to the text of Lees, on which see in the abbreviations section below.]
Harari, Yuval Noah. 2004. “Eyewitnessing in Accounts of the First Crusade: The Gesta Francorum and Other Contemporary Narratives.” Crusades 3: 77–99. [Questions how much of the narrative is really an authentic first-person report.]
Jamison, Evelyn. 1939. “Some Notes on the Anonymi Gesta Francorum, with Special Reference to the Norman Contingent from South Italy and Sicily in the First Crusade.” In Studies in French Language and Mediæval Literature Presented to Professor Mildred K. Pope, edited by Mildred K. Pope, 183–208. Manchester: Manchester University Press.
Morris, Colin. 1993. “The Gesta Francorum as Narrative History.” Reading Medieval Studies 19: 55–71.
Rubenstein, Jay. 2005. “What is the Gesta Francorum and Who is Peter Tudebode?” Revue Mabillon 16: 179-204.
On the First Crusade
Asbridge, Thomas. 2004. The First Cusade: A New History. Oxford; New York: Oxford University Press. [Highly readable; perhaps the best introduction.]
France, John. 1994. Victory in the East: A Military History of the First Crusade. Cambridge; New York: Cambridge Univeristy Press.
Frankopan, Peter. 2012. The First Crusade: The Call from the East. London: Bodley Head. [Also very readable; a consideration of the Byzantine perspective.]
Kostick, Conor. 2008. The Social Structure of the First Crusade. The Medieval Mediterranean 76. Leiden; Boston: Brill. [Contains a good chapter on the Gesta Francorum.]
Lapina, Elizabeth. 2015. Warfare and the Miraculous in the Chronicles of the First Crusade. University Park, Pa.: The Pennsylvania State University Press.
Riley-Smith, Jonathan. 1986. The First Crusade and the Idea of Crusading. The Middle Ages Series. Philadelphia: University of Pennsylvania Press.
Rubenstein, Jay. 2005. “What is the Gesta Francorum and Who is Peter Tudebode?” Revue Mabillon 16: 179–204.
Rubenstein, Jay. 2011. Armies of Heaven: The First Crusade and the Quest for Apocalypse. New York: Basic Books. [Available as audio book from Audible.com, etc. Also highly readable, with a particular interest in the mentality of the crusaders.]
Runciman, Stephen. 1951–1954. The History of the Crusades. 3 vols. Cambridge: Cambridge University Press. [The classic narrative; volume 1 is on the First Crusade.]
On medieval Latin in general.
Dinkova Bruun, Greti. 2011. “Medieval Latin.” In A Companion to the Latin Language, Blackwell Companions to the Ancient World, edited by James Clackson, 284–302. Chichester: Malden MA: Wiley-Blackwell.
Mantello, F.A.C., & Rigg, A.G. (eds.). 1996. Medieval Latin: an Introduction and Bibliographical Guide. Washington, DC: CUA Press.
A standard reference work for students of medieval Latin. On medieval Latin morphology and syntax see pp. 85-89.
Stotz, Peter. 1996–2004. Handbuch Zur Lateinischen Sprache Des Mittelalters. Handbuch der Altertumswissenschaft, 2. Abt., 5. T. Munich: Verlag C. H. Beck.
Strecker, Karl. 1957. Introduction to Medieval Latin. translated and revised by Rombert B. Palmer. Berlin: Weidmannsche Buchhandlung.
Dictionary of Medieval Latin from British Sources (DMLBS), available for free online through Logeion. Based on sources from Great Britain covering the whole of the Middle Ages, from Late Latin to humanist authors ca. 1500. Despite this regional focus, its accessibility, ease of use, and coverage of common medieval words and meanings makes the DMLBS an invaluable resource for readers of medieval Latin.