As noted in the link cited below, in addition to Chaucer, anonymous playwrights creating allegorical plays, the Pearl poet (The Pearl and Sir Gawain), Langland, and Mandeville would be important resources. The many writers, often anonymous, of Arthurian tales would have influenced Chaucer's and others admiration for romance. French writers (Marie de France and the troubadours) and Italian ones (Boccaccio) were also influential.

A major figure not often remembered is John Gower, a personal friend to Chaucer. Gower is famous for three poems—the Mirour de l'Omme (in French), Vox Clamatis (in Latin) and Confession Amantis (in English)—that likely influenced Chaucer. These moral poems include dream visions, frame narrative, and romance, also found in Chaucer's writing and in other poets of the era.

Gower drew subjects from history, politics, legends, and religion. Like many writers, he wrote allegories and ballads. He is often called "moral Gower," and appears in Shakespeare's Pericles as such.

Obviously, the most influential English writer during the age of Chaucer (basically, the second half of the fourteenth century) was Chaucer himself. He published the immortal (but incomplete) The Canterbury Tales in 1400, the year of his death, and the collection of stories became widely admired and very influential. 

Other influential English writers of the period include William Langland, who is credited with writing Piers Plowman sometime around the 1370s, and John Mandeville, whose quasi-fantasy account entitled The Travels of John Mandeville depicted the author's journeys through the Middle East and beyond. The "Pearl Poet," the unknown author of a poem by that title as well as, probably, the poem Sir Gawain and the Green Knight, is also a well-known writer from the period.

Other writers who were influential among learned circles in England included the Italian writer Giovanni Bocaccio, whose Decameron influenced The Canterbury Tales; and Petrarch, whose writings are actually mentioned by Chaucer. 

http://www.enotes.com/topic/Pearl_Poet