The zone 3-4 hardy cactus (Escobaria) is incredibly easy to germinate. If you have ever sprouted Mammallaria sp. seed, you know what I mean, as Escobaria is closely related and was once lumped in the same genus only 15 years ago.

Leibnitzia anandria is an interesting plant, but see this thread for some practical info.

Iris setosa ssp. canadense is a little dwarf species, prefering moist locations, but tolerating dry. 10-12 inches, flowers quite blue for an iris.