Midnight Blue Rose that I planted earlier this year, to compliment one called Agatha Christie, so named after the author. Agatha isn't blooming yet but I'll let you know when she does.
Some nice companions might be:
Rosa carolina, for it's brilliant pink color but apparently it spreads aggressively.
Asclepias tuberosa, for it's brilliant orange color.
Generally anything that goes with purple. Be warned with anything yellow though. Colors that are opposite one another on the color wheel will trick the eye into thinking they're vibrating. Perhaps that's another reason why the middle of the flower looks so intense. A larger bloom might lose the effect the center of the flower creates.