Here you can find links to primary materials for the Middle Ages (most hosted at Google Books). You can either read them online, or download the PDF to read at your leisure.
ELEVENTH AND TWELFTH CENTURY CHRONICLES:
The Anglo-Saxon Chronicles- Stevenson's translation of the roughly annual chronicle of England up to 1154. From the Church Historians of England, Volume 2, Part 1.
Florence of Worcester- Stevenson's translation of the twelfth century Chronicle of Florence of Worcester. An English chronicler who largely relied on the Anglo-Saxon chronicle, but who added his own details up to the middle of the twelfth century. Very valuable for Anglo-Norman history. From the Church Historians of England, Volume 2, Part 1. (NOTE- The real name of the chronicler was John, not Florence.)
Henry of Huntingdon- Forester's translation of the twelfth century Chronicle of Henry of Huntingdon. Henry, like John of Worcester, was an English chronicler who wrote in the first third of the twelfth century. Very valuable for English history.
Deeds of Stephen (Gesta Stephani)- An anonymous chronicle of the troubled reign of King Stephen, 1135-1154. It is part of the volume with Henry of Huntingdon, so scroll down to find it.
History of the Kings of England by William of Malmesbury- Usually considered one of the finest medieval historians. He wrote a history of the kings of England, culiminating in the mid-twelfth century. This is Stevenson's translation from the Church Historians of England, Volume 3, Part 1.
The Historical Works of Symeon of Durham- Stevenson's translation of the mid-twelfth century chronicle of Symeon of Durham. Symeon was a twelfth century chronicler from the north of England. Taken from the Church Historians of England, Volume 3, Part 2.
William of Newburgh- Stevenson's translation of the chronicle of William of Newburgh, an English historian writing in the late twelfth century. His chronicle is an excellent source for the reigns of Henry II and Richard I of England. Taken from the Church Historians of England, Volume 4, Part 2.
Robert de Monte- Also known as Robert of Torigni. He was a Norman monk who wrote in the late twelfth century. He is especially useful for continental affairs from the second half of the twelfth century. Taken from the Church Historians of England, Volume 4, Part 2.
John and Richard of Hexham- Chronicles from two monks of Hexham in the north of England. Useful for Anglo-Scottish relations especially. Taken from the Church Historians of England, Volume 4, Part 1.
Chronicle of Holyrood- A twelfth century chronicle covering events in northern England and southern Scotland. Taken from the Church Historians of England, Volume 4, Part 1.
Jordan Fantosme's Chronicle- An account of the 1173-1174 invasion of the north of England by King William of Scotland. Taken from the Church Historians of England, Volume 4, Part 1.
Richard of Devizes' Chronicle- An account of Richard I's reign by Richard of Devizes.
THIRTEENTH CENTURY SOURCES
Chronicle of Melrose- A thirteenth chronicle from southern Scotland. Taken from the Church Historians of England, Volume 4, Part 1.
Matthew Paris, Volume I- The first volume of Matthew Paris' English history, translated by J.A. Giles, covering the period from 1235-1244. Paris is the most valuable and famous of English historians from the thirteenth century.
Matthew Paris, Volume 2- The second volume of Matthew Paris' English history, translated by J.A. Giles, covering the period from 1244-1252. Paris is the most valuable and famous of English historians from the thirteenth century.
Siege of Carlaverock- An account of the nobles who attended Edward I's siege and capture of Carlaverock castle in 1300.
GOVERNMENT DOCUMENTS
Calendar of the Close Rolls- Close letters were documents sent by the King, or his officials, granting titles, powers, offices, etc to people in the kingdom. They were then enrolled onto government registers.
Calendar of the Patent Rolls- These are official royal pronouncements, issued openly, and then enrolled onto a register.
Calendar of the Charter Rolls- A roll containing all charters issued by the English chancery, beginning in 1199.
Pipe Rolls- Pipe rolls were the accounting of the "farm" of the county by the sheriff to the Exchequer.
Introduction to the Pipe Rolls
Pipe Roll for Henry II, 1158-1159