Interesting to hear what you grow for companion plants, Poly and Sherry!
My climate is quite a bit colder and also more wet, I suspect, but I too use roses, blue Fescue (Elijah Blue) and Heuchera. I've also found that Pincushion Scabiosa and Phlox subulata tend to form relatively well-behaved mounts which does not encroach on the irises (provided you plant them with enough space between them to start with of course - I'm learning that... I hope!
) Alliums also work well for me, because they look good and don't take up much room. I use Astrantias and Aquilegias too and they work really well, as long as you get those seeds before they drop! I have also just made a new mixed border with Tree Peonies, Peonies, Aquilegias, Dryas and a few irises (No new beds without irises!
), but have yet to find out if that will work or not.