A few definitions first: when one says "editorial comic" pretty much everyone thinks of something like this. Caricature + obvious summation of current news event + labels. It's a long tradition in America that continues to hold on in major newspapers. There's also a long standing thread of politically aware commentary in comics as a whole which one can trace back through Pogo all the way to The Yellow Kid. Somewhere in the middle is the group of comics that deals with comics and politics that mostly got its start in the weekly free newspapers that most major cities have.
None of these comics seem to have a success story with any indepedent webcomic model. (Please tell me if I'm wrong!) Lately however, I've seen some interesting changes: Tom the Dancing Bug has moved to Boing Boing, a very popular blog and a progressive blog, The Daily Kos, has started a comics section organized by Tom Tomorrow of This Modern World. It places these comics out of a "comics" context and more in the context of their point of view.
Also worth checking out is the first part of a Daily Crosshatch interview with opinionated cartoonists Ruben Bolling, Tim Kreider, and Ted Rall.