ChEMBL or ChEMBLdb

ChEMBL or ChEMBLdb is a manually curated chemical database of bioactive molecules with drug-like properties. It is maintained by the European Bioinformatics Institute of the European Molecular Biology Laboratory based at the Wellcome Trust Genome Campus in Hinxton, UK. The database, originally known as StARlite, was developed by Inpharmatica Ltd., later acquired by Galapagos NV. The data was acquired for EMBL in 2008. 

The ChEMBL database contains compound bioactivity data against drug targets. Data can be filtered and analyzed to develop compound screening libraries for lead identification during drug discovery. In October 2010 ChEMBL version 8 (ChEMBL_08) was launched, with over 2.97 million bioassay measurements covering 636,269 compounds. ChEMBLdb can be accessed via a web interface or downloaded by File Transfer Protocol. It is formatted in a manner amenable to computerized data mining, and attempts to standardize activities between different publications, to enable comparative analysis. ChEMBL is also integrated into other large-scale chemistry resources, including PubChem and the ChemSpider system of the Royal Society of Chemistry (text from wikipedia).

See also Norecopa's collection of links to alternatives databases