I didn't plant Oriental poppies in my gardens, they just showed up one day. And they thrived. So every year or so I divide the plants, and move them around, and now they're everywhere. They're very polite perennials, though. No overseeding or taking over, pushing other plants out of their way. They just set fuzzy green buds in the middle of spring, then one at a time, pop open into a riot of bright orange.
Since most of my choices for perennials are pinks and blues and purples, the orange fits in quite well.
But I think the bud stage steals the show. I just love those huge green spiky flower heads, just before the orange starts to peek through.