I came across a plant yesterday at a posh garden centre which I thought I'd share as it would be fab for a window box or as a tablepiece or something cascading down a mantelpiece etc.
Calocephalus
I saw it in smallish pots, one squished next to the other so the pots were hidden, fronted by small-leaved trailing ivy (again pots so close that you can't see them). Looked fab. Ethereal silvery, abstract shape. Lovely.
The photo doesn't really do it justice. I have no idea about hardyness / evergreen etc. I bought three because they looked wonderful.