Look! Look at this! It’s John Watson’s blog!
I haven’t read the most recent posts (help, spoilers!), and I suggest you don’t either if you haven’t seen Season Three yet. But it’s quite entertaining. Perfect if you need a Sherlock fix between seasons.
Oh, and Sherlock has a website, too. Not as much content, but he does use it occasionally to communicate with Moriarty–and there are some nice little puzzles to solve as well. Here you go!