allium (ornamental onion) 'purple sensation'

This variety is the earliest to bloom of the large, purple alliums, plus it survives the winter reliably and even self-seeds.  It's about 75 cm tall and I leave the dried seed heads standing all summer because they still look good.  You could also save them for dried flower arrangements.

Plant these in fall (from bulbs) in full sun.  You can see a relative, chives, just starting to bloom in the background here and I like how they echo each other.