the three most important cities (esp. in ref. to Tokyo, Osaka, Nagoya)
The Three Major Duties (education, work and payment of taxes)
the three grand national holidays (Prayer to the Four Quarters, Empire Day, the Emperor's Birthday; pre-1927)
three greatest teas of Japan (Uji-cha, Sayama-cha and Shizuoka-cha)
three major diseases (cancer, cerebral stroke, acute myocardial infarction)