Some of the earliest Iris that I know of here in the New York metropolitan area have just come up in the last couple weeks. These are different cultivars of Iris reticulata, a sensational early spring bloomer.
Weighing in at only 4-6" tall I see people miss these all the time but if you get down to their level you quickly realize they really pack quite a punch. Of course they still have that quintessential Iris flower with their upright standard and down-turned falls. And look at this guy with his deep purple and yellow-orange throat. Oh, fuggeddaboudit!
Iris like a whole variety of conditions based on the species and type of Iris, but these guys love a sunny spot with a decent amount of organics and drainage.