We love concrete at Sawa. Kast makes knobs out of concrete. Therefore, they are loved by us (or, at least by me)! I also enjoy that they all have lady names, it gives them a little bit of personality in my mind.
A few of my faves:
The knobs are cast by hand in Cleveland Ohio (Cleveland Rocks!) by a guy named Grey Hensey. You should check out the whole catalogue of products on his website.