See also secondary sources in English and Italian

Mirabilia urbis Romae (The Marvels of Rome), trans/ed. Francis Morgan Nichols, London, 1889; 2nd ed. with new introduction by Eileen Gardiner, New York: Italica Press, 1986.the earliest guidebook to Rome, supposedly written by Benedict, a canon of St.Peter’s, 1143.
Nichols, Francis Morgan, Eileen Gardiner, and Ronald G. Musto. The Marvels of Rome for the Macintosh. 3rd electronic ed. New York: Italica Press, 1993

Gregorius, Magister. [Mirabilia Romae. English] The Marvels of Rome / Master Gregorius, translated with an introduction and commentary by John Osborne. Toronto, Ont., Canada: Pontifical Institute of Mediaeval Studies, 1987.
Osborne, John. Ed and trans. The Marvels of Rome, Toronto: Toronto University Press, 1987.

D’Onofrio, Cesare. Visitiamo Roma mille anni fa: la città dei Mirabilia. Roma: Romana società editrice, 1988. Physical Details: 215 p. : 106 ill.; bibliogr., index. Series: Studi e testi per la storia della città di Roma; . Summary: Excerpts from four early guidebook descriptions of Rome, ca.1000-1410/1419, with notes and illustrations of the monuments commonly visited by Medieval pilgrims.

15th century
Leon Battista Alberti: Descriptio urbis Romae, c.1433

Flavio Biondo: Roma instaurata, 1444, published 1481.

16th century

Francesco Albertini: Opusculum de mirabilibus novae et veteris urbis Romae, Mazochio, Roma, 1510.

Andrea Fulvio: Antiquitates urbis, 1513

Bartolomeo Marliano: Topographia antiquae Romae, 1534.

Andrea Palladio: The Churches of Rome, 1554. modern edition, ed/trans. Eunice Howe, MRTS, 1991.

Five Early Guides to Rome and Florence, with introduction by Peter Murray, Gregg International Publishers Limited, 1972. includes facsimiles of guides written by Albertini and Palladio, as well as an  anonymous guide, published in Venice in 1480. Helpful introduction.
 

Guidebooks/Accounts of English visitors

The Stacions of Rome (Vernon Ms) Frederick J. Furnivall, ed., Early English Text Society: London, 1867; reprint Greenwood Press, New York 1969).  English verse account dated 1370. 

John Capgrave: Ye Solace of Pilgrims, ed. C.A. Mills, Oxford, 1911. Modeled on the Mirabilia urbis Romae, it is likely written shortly after Capgrave’s visit to Rome in 1450. He includes descriptions of ancient marvels in part I, and churches (the seven basilicas and other stations) in part II; in part III he focuses on the churches dedicated to Mary.
Capgrave, John. A Fifteenth Century Guidebook to the Principal Churches of Rome. trans. C. Evenleigh Woodruff. London: Marshall Press Limited, 1933

William Brewyn: A XVth Century Guidebook to the Principal Churches of Rome, trans. C.E. Woodruff, Marshall Press, London, 1933. reprint AMS Press, NY, 1980. Brewyn’s account dates to c.1470. Includes lengthy descriptions of the seven basilicas, a random assortment of other churches, a list of the stations, a transcription of a Papal Bull issued by Paul II in 1469 warning against harming pilgrims, and an itinerary of the route from Calais to Rome.

“A True Description and Direction of what is most worthy to be seen in all Italy...”, Harleian Miscellany, XII, 1811, 73-129. An anonymous manuscript, it most likely dates to around 1600.