And even before that (or possibly not before that), I remember going to emule to download what were essentially memes. A lot of them spreading partially via email.
But I think in the least 8 years, 4chan has really become the main birthplace of memes.
ADTRW was just the anime forum. The admins called it that to annoy the anime kids. They would all hang out on 2chan, the japanese precursor to 4chan.
FYAD was the forum with no rules. It was (is?) basically /b/ but this is back in the day so it was much smaller, everyone knew everyone else. It was basically a little clique that would sit there making injokes.
I never really went in there, but the notable thing about it was that the mods would constantly abuse the css and js on the forum theme to the extent that it would often crash some browsers. It was pretty funny. Oh, and there was always one mod who was elected from the userbase every month, the "idiot king" who would rule with an iron fist. In short, like online gaming, it would be great in theory except for the fact that everyone else there is an antisocial teenage nerd.
Also, the memes that originate elsewhere are still made popular due to 4chan's influence. e.g. "trollface" apparently comes from deviantart but is commonly used in rage comics (I think).
There are a few similar comic artists. Notably 3-Angled-Blue, who drew some amazing MS Paint comics that are slowly being made into rage comic templates.
Also, it wouldn't be fair to attribute all the things you've cited to 4chan only. Something Aweful contributed to the birth of many "early" memes for instance. And I think the rage comics were infamously made popular by reddit (4chan had "MS paint comics" and such).