Lucas McDonnell provides 31 essential knowledge management sites, which may end up growing beyond 31. (The URL suggests it was originally 26.) Most of these sites are blogs with a few other types of website that are frequently updated.
Sadly, a few of the sites listed aren't nearly as useful as they once were, either because they haven't been kept up-to-date or because their audience moved to other things.
Oh, and I am in the list. Thanks, Lucas!