The Complete Works of Geoffrey Chaucer, vol. 6 (Introduction, Glossary, and Indexes)
The late 19th century Skeat edition with copious scholarly notes and a good introduction to the texts.
The Complete Works of Geoffrey Chaucer, edited from numerous manuscripts by the Rev. Walter W. Skeat (2nd ed.) (Oxford: Clarendon Press, 1899). 7 vols.
The text is in the public domain.