I am a rather avid web comic reader with about two dozen of them wedged in to my current Google Reader page. Unfortunately, only a few of them can really be characterized as super powered strips. Say what you will about web comics, but diversity seems to be the name of the game with them. The superhero monopoly doesn’t extend in to this market.
Not to say that there aren’t great super powered webcomics.
Take for example, Spinnerette, a parody of Marvel superheroes and highly entertaining standalone strip in one great package. The comic has great manga style art, compelling characters and quite a bit of ribald humor. And with seven issues out of the way, it is easily one of the most prolific super powered web series out right now.