In addition to the traditional wheels available through the above site, Hal Reed's Analogous Color Wheel is a wonderful studio fundamental.
You identify what you see as the dominant hue in a scene/image/painting, and Hal's wheel shows the full range of analogous color, if this is the type of color harmony you are after. Cut-outs also identify color discords for any given scheme.
Available at
www.artvideostore.com or through (888) 513-2187.
Chris