A list of Reichenbach theories for anyone who's just finished s2e3 and wants to scream "HOW, Sherlock, how...???"
Some of these I've read, and some I haven't. (I'm erratic about where I end up on tumblr.) I can easily recommend the Final Problem's enormous and far-reaching RF theories, of course.
And the Sherlock candy: a blog series written by the marvelous MK Hey. You need to have seen both seasons or you'll be spoiled.
There's lots more, but take those as your starting points and you can't go wrong. 8)