Currently I'm reading the first volume of
The New Annotated Sherlock Holmes. The three volumes, edited and annotated by Leslie S. Klinger, include every single Holmes short story and novel written by Sir Arthur Conan Doyle. I'd read very little of the original Holmes stories before, and realized that was a significant lack in my reading. And I'm glad I'm doing so, as this is some great stuff.
(Some of the annotations are unintentionally hilarious. While a lot of them are simply explaining contemporary references -- which is quite useful for a reader who exists in a world 100 years away from Holmes and Watson's -- the ones that try to explain the numerous inconsistencies are absurd. People have spent a ridiculous amount of energy contorting themselves to try to explain away stuff that basically boils down to the fact that Conan Doyle was lazy with his technical details and wasn't copy-edited.

)