Black carpet with a white rug. Or maybe go red. Grey goes good with everything.
Blue carpet would look nice. Blue and grey go well together.
Bright orange is popular at the moment, and goes well with gray. For a more subtle approach I like medium blue through navy with gray. My favorite is cream, but this choice is usually better for a home without children or pets.
Tan ish pattern, or at least buy pillows with color so your carpet can match.
I have grey walls and blue curtains, what color carpet should I get?