For reduced-price air tickets at student- and youth-oriented travel agencies, the following cards are widely recognized:
ISIC student card
IYTC (under 26 years) card
ITIC card for teachers
Reduced prices for students and seniors on Mexican buses and at museums and archaeological sites are usually only for those with Mexican residence or education credentials, but the IYTC, ITIC and particularly the ISIC will sometimes get you a reduction.