This website from Rockefeller University in New York contains "a gene expression atlas of the central nervous system of the mouse based on bacterial artificial chromosomes (BACs)." GENSAT, or the Gene Expression Nervous System Atlas, contains brain slice images of BAC transgenic mice at the embryonic, postnatal (7 days old), and adult stages, stained to show areas of gene activity. The website comes with a detailed and helpful tutorial that recreates GENSAT's user interface and demonstrates how to manipulate search results.