Not pretty, but are more concealable than many other offerings...Hogue black "rubber?" grips. I find I shoot much more accurately with them, also.
I like the Hogues, myself, but for concealment, they're not optimum. They're long as they mount using a screw and stirrup arrangement at the bottom of the grip that makes 'em longer than most. Still, I find that under a baggy shirt, they're concealable, and I love how they feel. There are better grips purely for concealment, though, on a square butt. Really, it don't get a lot better than the thin Smith grips with a Tyler T grip adapter.
Ruger's grip design sure gives one a lot better options.