Gene Expression Omnibus (GEO)
As the site says: "This database stores curated gene expression DataSets, as well as original Series and Platform records in the Gene Expression Omnibus (GEO) repository. Enter search terms to locate experiments of interest. DataSet records contain additional resources including cluster tools and differential expression queries."
The site can be found at: https://www.ncbi.nlm.nih.gov/gds/