I have some extras of this neat (if aggressive) plant, it has beautiful giant foliage (mine grow to about 36" wide and 48" tall, they would probably get bigger in damp soil) and edible flowers and leaf stems.

Zone 5 Hardy Cacti
Apios americana (named cultivars only)
Rhodiola spp.
Turkish Rocket (Bunias orientalis)
Colewort (Crambe cordifolia)
Crassula "ivory tower"
Curculigo latifolia
Decaisnea fargesii
Delosperma basuticum (or other non-pink hardy delospermas)
Diplotaxis tenuifolia "discovery" (or other perennial arugula)
Echinocereus reichenbachii
Empetrum rubrum
Ephedra minuta, Ephedra regeliana or other zone 5 Ephedra spp.
Escobaria vivipara
Eucalyptus bridgesiana, E. neglecta or any other Eucalyptus that might stand a chance in zone 5
Euphrasia officinalis
Euphrasia stricta
Frailea castanea
Lathyrus vernus (looking for the wild blue changing to purple flower.)
Chupa Sangre (Maihuenia poeppigii)
Opuntia fragilis
Schisandra chinensis (named cultivars)
Alexanders (Smyrnium olusatrum)
Stephania suberosa
Symphytum "Goldsmith"
Synsepalum dulcificum
Thaumatococcus daniellii
Turbinicarpus jauernigii
Yucca rostrata
Zingiber mioga especially 'Dancing Crane' but i would try others.
Burr Oak "Maximus"
Sea Kale (named cultivars)
Pedicularis canadensis
pedicularis groenlandica
Sassafras
Kratom (Mitragyna speciosa)
Goumi (esp dwarf cultivars)
Seaberry (named cultivars only)
Rebutia arenacea
Honeyberry (named cultivars only)
kava kava (Piper methysticum)