I've finished reading Worm, a web serial about a world where superpowers are real, semi-recently and figured it was worth recommending. You can find it at
http://parahumans.wordpress.com/Fair warning: It's very dark. People die, many victories come at a price, heroes are not necessarily good, and villains are not necessarily bad. Everything is played as realistically as possible except for the superpowers, meaning that people get hurt a lot, and in ways that have long-lasting repercussions. It's also VERY LONG. The format was releasing a new update every couple of days, which means that although the world and characters in it are very detailed, it takes a long time to get through.
My one complaint is that the story runs on throwing harder and harder opponents at the protagonists. There are also a couple things that show up in the last couple of arcs that bug me. However, there are enough "holy shit that was amazing" moments in it to make it worth it.
Edit: You know what actually just read
http://parahumans.wordpress.com/about/ it's far better than the description I gave.
