Friedberg is the standard edition (in two volumes): Aemilius Friedberg, ed., Corpus Iuris Canonici, editio Lipsiensis secunda, 2 vols. (Graz: Akademische Druck- u. Verlagsanstalt, 1959).
Friedberg is online and downloadable, with shortcuts to the beginning of each part:
http://www.columbia.edu/cu/lweb/digital/collections/cul/texts/ldpd_6029936_001/index.html
http://www.columbia.edu/cu/lweb/digital/collections/cul/texts/ldpd_6029936_002/index.html
FIRST REFERENCE IN A CHAPTER: Decretum Gratiani 1.12.123, in Aemilius Friedberg, ed., Corpus Iuris Canonici, editio Lipsiensis secunda, 2 vols. (Graz: Akademische Druck- u. Verlagsanstalt, 1959), vol. 1, cols. 15–20.
SUBSEQUENT REFERENCES: Decretum Gratiani 1.12.123, in Friedberg, Corpus Iuris Canonici, vol. 1, cols. 15–20.
Zeeden, Faith and Act, 84f: many Lutherans retained Canon Law where it did not contradict Scripture. {Ben’s dissertation confirms this re: marriage}