Anonymous
This loose group of Internet vigilantes (vaguely centered around, but not officially connected to, the site 4chan) often harasses unsavory but small-time people, but they did help with the arrest of pedophile Chris Forcand. Their usual tactic is a simple denial of service attack like the one against Scientology.org, but they occasionally get more sophisticated; members tell me they plan to hoist banners above some Church branches. Inspired by the release of Tom Cruise's secret Scientology video and the Church's attempts to suppress it, Anon promises an all-out war in the following hokey but entertaining video:

Digg
The users are less aggressive, but Digg is a promotion machine for stories users feel are overlooked by the media. They love to stick it to the man, and they love the freedom of information. That's why the many popular Scientology criticisms on Digg focus on the Church's history of censorship. Digg promoted the Cruise video, but they gave much more love to the Church's takedown letter to Gawker.

YouTube
The Church got the Cruise video removed from the site, but within a few days a new copy was up. Meanwhile there are plenty of parodies less likely to be deleted. The Church may have plenty of money to litigate, but if it tries to force the issue with YouTube, it'll find itself up against Google, which loves fighting bogus copyright claims.

YTMND
The site is usually just a jumble of in-jokes, but after several users mocked Scientology's mythology, user Smoothmedia designed a presentation accusing the Church of destroying several lives and harassing critics. There's a copy on YouTube (which was popular on Digg, natch):

Mainstream media has criticized the Church too, but the most famous examples are parodies from comedy shows like South Park (in an episode later censored by Comedy Central) and Craig Ferguson's Late Late Show (which still didn't run footage from the actual video). Maybe media outlets don't want to lose pull with Cruise and his celebrity friends, or maybe they just don't care, but the Internet's doing a great job exposing the dangers of the cult. Thank Xenu for immature Internet teenagers!

Encyclopedia Dramatica:
The Wikipedia of obscure Internet memes, particularly those on the sites that follow. ED is run like Wikipedia, but its style is the opposite; most of its information is biased and opinionated, not to mention racist, homophobic and spiteful, but on the upside its snide attitude makes it spot-on about most Internet memes it covers. However net-savvy you are, ED is edgier, and it will perform 2 girls 1 cup on you to prove it.

4chan:
An English-language forum based on what is possibly the largest forum in the world, the Japanese 2channel. While 4chan's topic areas cover several aspects of Japanese culture, anime, and plenty of dirty hentai, the only board that matters is /b/.

/b/:
A subset of 4chan, technically a "random image board," where completely anonymous — no login, no username — people try to shock, entertain, and coax free porn from each other. Encyclopedia Dramatica calls it the asshole of the Internet. It's where LOLcats started as the edgier, funnier Caturdays, in which photos of cats (particularly on Saturday) were posted and captioned with forumspeak, which degenerated into the LOLspeak you now think is so clever.

Customs on /b/ include posts promising photos of personal degradation in return for certain kinds of porn or other helpful information; sarcastically asking for advice on teen romance; sarcastically asking/telling anything; pretending to have insider info or be privy to breaking news; posting image puzzles; and raiding other people's sites. Major media coverage is always full of fear and loathing, and is sometimes hilarious, as in this investigation by the Fox news reporter who played himself on Arrested Development:

/b/ has no rules; pretty much the only thing guaranteed to get a user banned is child porn, and even that gets constantly joked about. Reading /b/ will melt your brain, but sometimes you need that. It's like how I can't start a rough draft without a beer, but the analogy works better with heroin mixed with fiberglass.

Something Awful:
A comedy site on the level of Ebaum's World, Fark or College Humor. SA specializes in full-length articles about pop culture and weird web sites. The site is at its best when it mocks bizarre forum writers, such as this string of weird posts from Dogster, where users often post in character as their dogs.

YTMND
It started with this web page, a sound bite looped over an image and some floating text: "You're the man now dog!" YTMND creator Max made it after seeing Finding Forrester and pinpointing the "you're the man" line as the moment Sean Connery lost his dignity. He then made a site for other such mini-pages, which have evolved into mini-movies. The site, like any decent forum, developed a rich set of in-jokes, especially because interaction relies on creating a little mesh of several concepts. Popular in-jokes include Star Trek's Captain Picard (personal favorite: "The line must be drawn here!"), a joke about Mike Tyson's Punch-Out and the phrase "Nigga stole my bike," and a song called "Bake a Pretty Cake" from a kids' show called "Lazytown." The Lazytown character Stephanie (pictured) has inspired deep research on YTMND into ages of consent around the world. Stephanie and other fads are constantly recontextualized and mashed up with each other; for example, "Bake a Pretty Cake" works well when played over a flaming body fleeing a burning building with the words "She didn't do the cooking by the book." It's like mashups only with less of the creeping feeling that you're just listening to two crap dance songs at once. Actually, it's exactly like that.

YTMND culture is much less abusive than 4chan but less accessible than Something Awful; it's another of the early churners of fads that haven't yet popularized on Fark, Digg, and Boing Boing.

Moral: You're not old, Gabe, you just have more comprehensible sites to read.
And barely any of "the kids" are reading the sites above; most of them are glittering out their MySpaces. Right, I think that covers the most important fad factories that most people haven't heard of. If you need more sites explained so you don't have to actually visit them, or if you really want an exploration of MySpace glitter culture and a definition of "Thanks for the add," e-mail me at nick at toomuchnick dot com.