NOAA
Noaa: Pmel: El Nino Theme Page
The National Oceanic and Atmospheric Administration (NOAA) sponsors this El Nino and La Nina resource site that features current and historic information about these weather systems with diagrams.
PBS
Pbs: El Nino
You can link to the anatomy of El Nino, chasing El Nino, and El Nino's reach. There is a resource page and a search page.
Science Education Resource Center at Carleton College
Serc: Detecting El Nino in Sea Surface Temperature Data
Through data analysis and observations of patterns, students learn about normal seasonal sea surface temperature variation as well as extreme variation, as in the case of El Nino and La Nina events, in the equatorial Pacific Ocean.
Climate Literacy
Clean: Ocean Impacts on an El Nino Event
Students examine the relationships among sea surface height, sea surface temperature, and wind vectors in classifying the ocean characteristics of an El Nino.