Mass Spectrometry

American Society for Mass Spectrometry http://www.asms.org/

Commercial Ambient Mass Spectrometers

Mass tech (AP MALDI) http://www.apmaldi.com/
Ionsense (DART) http://www.ionsense.com/
Prosolia (DESI) http://www.prosolia.com/

General Chemistry

NIST Webbook http://webbook.nist.gov/chemistry/
Database of small molecules with pertinent information (such as structure, mass spectrum, FTIR etc) maintained by the National Institute of Standards and Technology's (NIST).