If you look at my comics list on the site, you’ll see that the Official Handbook of the Marvel Universe and DC Who’s Who are some of my favorites. There’s something about having all of that information in one place. The bad thing about them is they become outdated even before they are published.
You can find entries on popular heroes on Wikipedia, but noting exhaustive. I once had a friend that asked me about setting up and online version of those old books, but we never got around to it. As I started messing with some Wiki software, I thought that would be a great project for it and it looks like someone else did too.