color management - Where can I find good test image(s) to send to a print lab?

I am looking for a good test image to send to a print lab, to test my system's color calibration.

I'll be sending my own photos too, of course, but I would also like to include one or two test images to exercise the process (and my knowledge of color and color problems) more thoroughly than my own photos might.

Answer

Here is the one we suggest using at SmugMug, the full sized image is available for anybody to use.

http://cmac.smugmug.com/SmugMug/Test-prints/Calibration-prints/122238_UAxBs#5637776_3P7qj-A-LB