I'd say 'Coral Fay' and 'Duchess de Nemours' are about the earliest in my garden. They are in peak bloom now. They had fully set buds by the end of April. I'm in zone 7. I would disagree with 'Karl Rosenfeld' as an early bloomer. Mine are not open just yet...

I second 'DnN' as the earliest of the common. KR bloom at least 2 weeks later for me in about the same time as Sarah Bernardt.

Reddbuffalo:

You might consider the "Memorial Day" peony - otherwise known as Paeonia officinalis 'Rubra Plena'. You can find it at a few sources - that I've discovered so far - and the direct link to both are listed below.

http://www.hirts.com/cgi-local/catalog.cgi?cat=1,41,&item=3079

Hirt's offers this information:

"Sumptuously full and richly colored, these long-lasting deep-red double flowers are large and luxurious. This well known Memorial Day peony blooms about week later than P. tenuifolia. Thrives in rich, well-drained soil. Very nice in borders, as hedge, or accents in front of walls, shrubs or fence. Full Sun. Zones 3-8."

My mother grew this peony for decades and often made use of it as a scented cut flower and it did bloom on, near, or around Memorial Day, but then she lived in central Illinois (Peoria) and now my daughter, Heather, has it in her garden.

The other source for this peony is peonygarden.com. The direct link to this peoney is listed below.

http://www.peonygarden.com/GARDEN%20HERBACEOUS%20PEONIES/RUBRA%20PLENA%20325.htm

You may note that their photograph isn't all that good and that their prices are much higher.

Unfortunately, I can't provide you with the reliability of either company; hopefully someone else in the forum can be of assistance on this manner. As for me, I'll probably place an order with Hirt's and see what happens.

If you're one to explore and research information, you might find the following source to be of assistance as well. It's the Kemper Center for Home Gardening at the extraordinary Missouri Botanical Gardens in St. Louis.

The direct reference/link is to one of the two peonies that I am considering adding to my garden this fall.

http://www.mobot.org/gardeninghelp/plantfinder/Plant.asp?code=Q260

They also have information on Karl Rosenfield. Here's the direct link.

http://www.mobot.org/gardeninghelp/plantfinder/Plant.asp?code=Q270

Heartland has a list on their site under bloom sequence of the average time based on the middle blooming plant,Red Charm. The url is http://peonies.org/