Aetna Intelihealth
Aetna: Inteli Health: Asthma
Thorough overview of asthma. Includes information on symptoms, treatment, prevention, and much more.
Mayo Clinic
Mayo Clinic: Asthma
This is a great starting point for anyone doing research or a report on asthma. Organized into several sections -- including "Signs and Symptoms," "Screening and Diagnosis," and "Treatment."