BioMart Perl API
BioMart is a great service for looking up just about any bit of info on just about any gene in just about any database. Perl API's let you automate these lookup tasks so you can script them or run large numbers of queries.
For more details, see the biomart documentation
An example script using Biomart API's to fetch gene info given an Ensemble gene ID:
Version 0.7 is installed on Fourierseq as of 6/16/11 by SPHS.