I used the standard color and gamma test charts to evaluate the performance of various papers. They were a good tool to judge technical qualities such as texture, color, gloss differential, etc. These charts helped me narrow down 100 papers to 10, but did nothing to help me artistically.
So I selected the following images for print testing (I download the full res images from www.pixel-peeper.com
You can right click on the image to download the full res original) This really helped me decide which paper looks best with which subject material. For example, the White Flower images looks great on Exhibition Fiber but awful on BC Vibrance Rag, while the violet flower image looks better on BCVR (as well as showed my inkset's color gamut weakness). The cat portrait looks surprisingly nice on Ilford Smooth High Gloss. If anybody has images that make great test prints, please share.
Black leather shoe: B&W, very fine detailhttp://www.flickr.com/photos/80903634@N00/8233198467
Violet flower: Vivid color, out of gamut violethttp://www.flickr.com/photos/43541511@N05/7546617122
White flower: B&W, pure white subject, no texturehttp://www.flickr.com/photos/57254022@N03/8089691899
Cat portrait: B&W, both soft and detailedhttp://www.flickr.com/photos/ballwell/4019123482/sizes/o/
Blond girl portrait: Color, blond hair & pale skinhttp://www.flickr.com/photos/98502433@N00/4061664664