Here's a list of some plants that will grow in Zone 5.

Flossflower
Pink Flowering Almond (Prunus glandulosa)
Hybrid Columbine (Aquilegia)
Adams Crabapple (Malus 'Adams')
Grape Hyacinth (Hyacinthus orientalis 'Gypsy Queen')
Peppermint (Mentha piperita)