Marquis who's who on the web - http://marquisewhoswho.com

Martin Dale's Center - http://martindalecenter.com

MasterFILE Premier - http://www.nclive.com/

Materials business file - http://www.csa2.com/ 

MathSciNet - http://www.ams.org/ 

Mechanical engineering abstracts - http://www.csa2.com/

MedHist - http://medhist.ac.uk/

MEDLINE - http://www.csa2.com/

Mental measurements yearbook - http://www.ovid.com/ 

Mergent online - http://www.mergentonline.com/ 

METADEX - http://www.csa2.com/

Meteorological & geoastrophysical abstracts - http://www.csa2.com/

Microelectronics packaging materials database (MPMD) - 
http://cindasdata.com/ 

MicroPatent materials patents - http://www.csa2.com/ 

Middle English compendium - http://www.hti.umich.edu/m/mec/ 

Military & government collection - http://www.nclive.org/ 

MLA directory of periodicals - http://www.ebscohost.com/

MLA international bibliography - http://www.ebscohost.com/

Morningstar.com. Library edition - http://www.nclive.org/

Mouse genome informatics - http://www.informatics.jax.org/