American Society of Mammalogists 

ASM Mammalogists on E-mail.  Searchable directory of mammalogists throughout the world.  You can search by name, institution, city, state, or country.

Checklist of Mammals North of Mexico: Pdf of Baker et al. 2003.  Revised checklist of North American mammals north of Mexico, 2003.  Occasional Papers, Museum of Texas Tech University, 229:1-24.  This is the most up to date list of mammals in North America.

Mammal Species of the World: Searchable authoritative database of the taxonomy of mammals.  Includes general information on distribution and status.  Includes standardized common names.

North American Mammals: A searchable field guide to the mammals of North America 

Mammalian Species: Mammalian Species is a peer-reviewed publication series of the American Society of Mammalogists.  Each volume is an account that summarizes available information on a particular species.  This site includes an index to the accounts and downloadable pdf files.