What are the best reference books in studying medieval England? (In terms of trying to expand your vocabulary and understanding of this time period?)
When are you looking? How early/late?
As a rule, I'd always recommend Britnell & Hatcher's Progress and Problems in Medieval England, Gillingham's The English in the Twelfth Century and Stenton's Anglo-Saxon England.
I'd also recommend Christie and Creighton's Transforming Townscapes.