Ptilostemon hispanicus has sat quietly and grown slowly for years; here in bud for the first time. I have wooed over its golden midribs and spines; but the bicolor phyllary spines have been worth the wait. Is it wrong to grow this? It's no spinier than a prickly pear (Opuntia) and it's been sited as such: well beyond arm's length in a rock garden bed.
I don't know if Staehalinia dubia is actually a thistle, but it shares that appeal. It is a small shrub about 10" (25cm) tall and wide; look close at those bits which make up the flower heads (phyllaries). No spines.
Leuzea conifera. Thanks for the seed, Bob. (syn Centaura, or Rhaponticum coniferum)
It has no spines, does not spread, and it is rugged and long lived.
And just for fun, not a thistle at all, but recently assigned under the morning glory family:
This is the parasitic "Farmer's Dodder," Cuscuta sp. (formerly known as?)
I don't see it often in field around the valley, and I've never seen it, until now, in one of my landscapes! (Swallowing Eriogonum corymbosum)