Rich sent me Pawprints on My Heart as a sdlg to test for him before introduction, it has been a great performer here as well. Bringing color other than yellow to the early season with great branching and budcount. A few other daylilies that have been here for more than 5 years and always performed well...
Astral Voyager - the first that comes to mind when someone asks me about hardy daylilies that don't just survive zone 4, but actually thrive in zone 4.
Big George - wonderful big, bright golden yellow double that often reblooms for me.
Broadway Valentine - Bright, clean colored red on a fabulous plant.
Dragon King - another fabulous red, branching/budcount can seem low when compared to newer cultivars, but still worthy of a spot in the garden.
Elegant Candy - one of my favorites of the early "candy" series, great branching/budcount when in full sun.
Fitzasaurus - big red spider, my clump is always loaded with blooms.
Itsy Bitsy Spider - one of the first to bloom here every year. Amazing in a clump!
Mystic Pizza - simply awesome! This one can't be missed even from far away, large flowers and the color is fabulous.
Noble Lord - an older clear saturated purple-red with a white wire edge. Growing on the corner of a bed that gets afternoon shade.
Rock Solid - the color can be a bit muddy sometimes, but it is always loaded with blooms...and a great parent for bringing hardiness into those southern patterns.
Spacecoast Tiny Perfection - makes a nice clump for the front of the border.
Vanilla Gorilla - super plant habit, big cream UF blooms.
There are many others that I will add once I get a chance to go through my plant list.