Obviously something stylish, clean, no logo, just a design element perhaps something along the line of Paul Smith stripes. The design element should not overpower the card, perhaps a line at the top, bottom or side. Type should be clean, but with a bit of an edge, easy to read. Colours could be black, taupe, dark blue, bronze. A hit of dark red never hurts either. My style is pretty eclectic but not trendy.