Geography Monkey (www.geographymonkey.com) is an excellent resource I have consulted a few times in the past (Credit to Tom Sheard, website creator).
I used some of the resources he collated on ENSO/La Nina/El Nino which clearly illustrate how these processes occur. Here is a link to it: http://geographymonkey.com/2-oceans-and-climate.html?m
