BioCyc - A collection of biological databases (http://www.biocyc.org/)
MetaCyc - Encyclopedia of metabolic pathways  (http://metacyc.org/)
Reactome - Curated database of biological processes in humans  (http://www.reactome.org/)
Brenda - The Comprehensive Enzyme Information System (http://www.brenda-enzymes.info/)
KEGG - Kyoto Encyclopedia of genes and genomes (http://www.genome.jp/kegg/)
BioPAX - Biological pathways exchange (http://www.biopax.org/)
Pathguide - the pathway resource list (http://www.pathguide.org/)