Ellis Peters "Cadfael" series, about a monk who's a medieval sleuth, is delightful, and a set of books that I often return to. She also wrote historical fiction under her real name, Edith Pargeter.
The Gwynnedd Quartet is about Llywelyn the Last, while the Heaven Tree trilogy is about the building of a great church in the 13th century. They're beautifully written and carefully researched, but are rather more serious (and sometimes heartbreaking) than the Cadfael books.
I don't know if they're available as e-books, though.
And if you're interested in books set in Victorian New Zealand... check my sig
