Specifically for me: I had heard about protein-sparing modified fat fasts (from the Dr. Atkins book) as I had been Atkins-style low carb for many years. I was searching for information via google on whether there was any new information on the protein-sparing studies in order to determine if it would really "wreck my kidneys" or "give me a heart attack".
While searching, I accidentally stumbled upon a link about the paleo "diet" (might have been "caveman" diet) and also the hyperlipid blog. At the time I was running about 30 miles a week so I went to the Runner's World Forum and looked for threads about running and eating a high fat diet. I posted a comment and a really nice guy who lived in Brazil told me to go to paleonu.com if I wanted to really get healthy. I read all of Dr. Harris's posts and also signed up for Mark's Daily Apple. I played around with paleo for awhile, not really too seriously---mostly just continued Dr. Atkin's style with a little more attention toward eliminating gluten. Then I saw Food Inc and King Corn, and everything just clicked. I bought GCBC, found paleohacks and have never felt better.
What specific web sources, books, movies or people made you change your way of eating?