I've only gardened in zone 6, so I can't speak from experience. But Swallowtail lists quite a few as hardy to zones 3 or 4 http://www.swallowtailgardense...
Hi Caitlin. There are many that will grow in zone 4. Have you been through the sedum database here at All Things Plants? It has a nice selection of sedum listed with photos and information. http://garden.org/plants/brows...