Antitussives are agents which suppress the act of coughing as opposed to suppressing productive coughing
Regular Websites
About.com: What Are Antitussives?
Contains the definition of antitussives, details about over the counter medications of this type, and specific antitussives, including Delsym and Robitussin DM. - About.com: What Are Antitussives?
http://coldflu.about.com/od/glossary/g/antitussives.htm
Anti-Tussives and Expectorants
Consists of a list of antitussives, their uses, mechanism of action, and dosages as well as other pertinent information. - Anti-Tussives and Expectorants
http://www.globalrph.com/anti_tussives.htm
Goes into some detail about antitussives, their classification, how and why they work, and what the indications are as well as the mechanism by which they function. - Pharmainfo: Anti-Tussives
http://www.pharmainfo.net/nirupama/anti-tussives