RTMark.com
If you can't fight 'em, join 'em, then fight 'em more effectively. RTMark (pronounced art mark) became a corporation so they could facilitate acts of corporate sabotage. They spotlight the essential injustice in the corporate entity (that it has all of the rights of the individual, but none of the responsibilities) by using their privilege of limited liability to veil monkeywrenchers -- while stating that one of their ultimate aims is to do away with the concept of limited liability. A brilliant paradox and the most inspiring site I've ever seen.

BlackEnvy.com
The folks at Guerrilla Media in Vancouver have made this site for those who are "profoundly envious" of Conrad Black, Canada's reigning media tyrant and owner of the National Post. GM is known for its polished, well-executed media actions, and their timely spin on the news translates well to the web -- and they get to push their satire to the technological limits.

KillZine.com
OK, so it's not actually finished yet. But this ambitious project (which spun out of the Kill Zinester tour of a while back) is a godsend for anyone interested in going beyond photocopying -- there's tons of valuable, first person publishing accounts. Mostly focused on the magazine end of things, anyone who found this site's "You should make one, too" section useful should definitely check out this one. The extensive plain-English glossary of printing terms alone make it worth your while.

Adbusters.org
Since I worked on one of the first versions of this site in '95, Adbusters has always used the web for their own subversive purposes: from the "Click Here To Send A Nasty JPEG To Philip Morris" actions of my day to the far more sophisticated multimedia treats on their current site. Still one of the few great magazines that has a site that's more than an online marketing tool.