Man, Usenet had the best online discourse - hardly any angry personal flaming because people dared to disagree. And Twitter, wow that was just pure rationality. slashdot - practically a masters program.

Now, they all did have gems of interaction that would could find by sifting thru the dumb stuff, but I find that property of discourse to be pretty steady. I've even found some interesting comments on YouTube videos and newpaper websites.