Tough to choose five! I have to go with the ones that are most successful in my garden with heavy neutral soil and fairly low rainfall, tolerant to frost. Also those with attractive foliage and that don't also grow in sun, that helps me to eliminate some favourites like Aquilegias, Violas and Astilbe.
Hellebores
Epimediums
Heucheras
Pulmonaria
Brunnera
