Reynolds SST analysis/anomalies
These images are updated automatically at the start of every month. Information on the Reynolds SST analysis, otherwise known as the NOAA Optimum Interpolation Sea Surface Temperature Analysis, can be found at http://www.emc.ncep.noaa.gov/research/cmb/sst_analysis/. Anomalies are calculated from a 1971-2000 climatology as described here.
Thanks to Liam Gumley for his code for plotting the GSHHS - Global Self-consistent, Hierarchical, High-resolution Shoreline data.
El Nino analysis
Above is a list of NINO indices and subsequent El Nino events based on "An operational definition of El Nino" (PDF) paper. The reference for this paper is: Reid,P.A. (2003) "An operational definition of El Nino", 7th International Conference on Southern Hemisphere Meteorology and Oceanography, 22-25th March, 2003, Wellington, New Zealand, p128-130. Data used to calculate the indices are from the Renold's SST anomalies above. Note that this list and definition are for research purposes only. For the Bureau of Meteorology's information on El Nino see their excellent climate section.