Gene Paint image library
I came across this lovely resource today.
Expression patterns are determined by non-radioactive in situ hybridization on serial tissue sections.
The database is gene-centric and entries can be searched either by gene name, accession number, sequence homology or site of expression. The website features a “virtual microscope” that enables zooming into images down to cellular resolution.
It has incredibly high resolution images (down to cellular level if you zoom in enough) showing amazing embryo sections with in situ staining for a huge set of genes.