Understandable IDs:
Gene name/symbol; for human, see http://www.genenames.org/
ENSEMBL gene/peptide;
UniProt/SwissProt/TREMBL ID/AC;
OMIM ID (human only);
RefSeq protein;
GI identifiers;
GO term;
KEGG pathway (format: KEGG#####);
EC number;
LocusLink (human/mouse/rat);
Zfin ID, AC, XPAT (D. rerio);
Affymetrix and Agilent microarray ID (D. rerio);
Aniseed, JG1 v.2, EntrezGene (C. intestinalis);
FBgn (D. melanogaster);
WBGene, WormBase (C. elegans);
SGD ORF (S. cerevisiae);
AGI locus (A. thaliana).