Are there any databases for gene co-expression or expression pattern clustering?

I am currently working on gene clustering based on co-expression pattern in mouse brain. The problem is I do not have some solid way to test my result. Are there any suggestions for databases indicating groups of genes that co-express (in mouse brain), or even better indicating some similarity metrics between each pair of genes based on expression pattern?

Also, I do want some databases for differentially-expressed genes 😉

PS: By "differentially-expressed" I am referring to a pair of genes whose expression patterns in a single individual differ.