Publications on ortholog dabases

NCBI COG and NCBI KOG
A genomic perspective on protein families. Science 1997 Oct 24;278(5338):631-7
The COG database: an updated version includes eukaryotes.BMC Bioinformatics 2003 Sep 11;4(1):41

OrthoMCL DB
OrthoMCL-DB: querying a comprehensive multi-species collection of ortholog groups. Nucleic Acids Res. 2006 Jan 1;34(Database issue):D363-8.

MultiParanoid
Automatic clustering of orthologs and inparalogs shared by multiple proteomes. Bioinformatics. 2006 Jul 15;22(14):e9-15.

TIGR EGO
Cross-referencing eukaryotic genomes: TIGR Orthologous Gene Alignments (TOGA). Genome Res. 2002 Mar;12(3):493-502.