Pulsatilla are great rock garden plants and any species or cultivar will make a good addition to your garden. They all flower early, and then produce lovely hairy seed heads. Pulsatilla styriaca is one of the earliest pulsatilla to bloom.
Yucca glauca, an agave, is the hardiest yucca growing from Alberta, Canada all the way to Texas. You will either love or hate this plant depending on your appetite for desert-like plants. I love them for their spiky leaves and fantastic flowers. They are extremely drought tolerant and easy to grow.
Paeonia rockii is a lovely tree peony that should be grown more. It can be difficult to find in a nursery, but those specializing in peonies will have it. The ones pictured here were grown from seed obtained from the Ontario Rock Garden Society Seedex program. The flowers are mostly white or light pink with dark maroon basal flares on the petals. There is some variation in flower form and coloration. One seedling from this group has red leaves in early summer.
The common name, tree peony, describes the woody stems that are produced, but it is probably more correct to call these shrubs, not trees. They do not need staking.
Mention lamium to most gardeners and they run for the hills. Some lamium spread so fast they are thugs in the garden. Others, like L. maculatum, spread but can be controlled. A few are excellent, well behaved, garden plants and this includes Lamium orvala, which forms a nice non-spreading clump. It might seed around a bit, but it is easily pulled out if you get too many.