It is an unfortunate fact in the study of church history that the early medieval period has been completely ignored. The time from the death Gregory (aprox. 600 A.D.) through the beginning of the scholastic period (aprox. 1100 A.D)is skipped over because there were no major theological advancements. In this period, the Western Church largely still followed Augustine, and not much theology was formulated beyond the words of Scripture and various compendiums of Patristic thought.
There were some extremely interesting disputes and figures within these so-called "dark ages." There were debates about the nature of Christ's presence in the Eucharist (between Ratramnus and Radbertus), the nature of predestination and the atonement (the Gottschalk controversy) as well as certain figures who challenged developments in the medieval church which went beyond Scripture (Claudius of Turrin for example). One figure who was influential in this period was Alcuin of York.
Alcuin was an 8th century British monk, writer, and teacher. He taught at the cathedral school at the time of Charlemagne, who he soon befriended. Alcuin became Charlemagne's chief theological adviser. His life was public, being both an ecclesiastical and political figure. Alcuin's writings were primarily influenced by the great bishop of Hippo, St. Augustine, as well as his British predecessor, the venerable Bede. He also drew heavily upon the writings of Gregory the Great.
Alcuin was most importantly, a devoted student of Scripture. Biblical allusion and quotation is abundant in his writings. There is most especially a devotion to the Psalter. Alcuin's methodology involved an intense study of the Biblical text, along with reference to various Patristic commentaries. In this way, my own preaching preparation is similar to that of Alcuin. Alcuin is also an important voice in the history of liturgics. Many of his prayer manuals became prominent in the medieval church, and some of his prayers were adopted at public worship services. It is likely that the celebration of All Saints day comes from Alcuin's influence.
Alcuin's works fill two volumes of the Patrologia Latina, and have unfortunately mostly not been translated into English. There is a small collection of writings and prayers which are available in English translation in the volume A Mind Intent on God by Douglas Dales. I have found this volume extremely edifying in my own life. Here is an example of Alcuin's prayer:
"Almighty Lord God, eternal and ineffable, without end or beginning: I confess you to be one in Trinity and threefold in unity: I adore you alone; I praise you; I bless and glorify you. I give thanks to you, O merciful and compassionate one, that you have granted me to lay aside the treachery and error of my spiritual night, and enabled me to participate in your grace. I beg you, O Lord, to perfect in me the work of your mercy that you have begun. Grant me always to think, speak and do what is pleasing to you. Guard me always and everywhere with your gracious care; and enable me, unworthy and wretched as I am, to come at last to the vision of your glory." (pg. 11)