The UniGene resource includes a Digital Differential Display, a computer method for comparing the expression of genes between different types of cells (e.g., cells from different organs, or cells from different stages of cancer).
For example, you can compare the differential expression of genes in liver, lung, muscle, and spleen:
The image above is an excerpt from:
Cancer Genome Anatomy Project (CGAP), Digital Differential Display, "Try this: Compare organs of the body," July 21, 2000.
http://www.ncbi.nlm.nih.gov/cgi-bin/UniGene/ddd?ORG=Hs &Pool1=Liver:155&Pool2=Lung:152&Pool3=Muscle:272&Pool4=Spleen:154 Pool4=Control:162+235.