Birkenstocks or Keens. I have a fantastic pair of Keens that are sort of like a maryjane. And I have about 6 pairs of birkenstocks which are amazingly comfortable.

Try somewhere like the Paddy Pallin website for some ideas of the different walking shoes about (they have some that are designed to be the only pair of shoes that a traveller takes with them so they have to be multipurpose).