A classic, of course, is this monster blob Ward Shelley did on The History of Science Fiction back in 2009. It has a small offshoot for Fantasy as well, although it's sketchy and leaves out some important works, so I'd like to see one done exclusively for the Fantasy genre. But if you're really into Sci-Fi and want a historical overview of what to read, this one is as good as any. Shelley, by the way, does charts reminiscent of the epic Wall Chart of World History by Edward Hull back in 1890, of which I have a facsimile edition. I like the style, and the overall graphic representation of a sci-fi alien fits it perfectly.
SF Signal just recently did one on the Hugo Award that has some interesting historical points as well. Along with a nice historical overview of the award and six of the major winners, it has a timeline that points out some of the major works and authors in the genre, as well as breaking down some stats about the award categories.
And finally, Goodreads just did one back in March on Dystopian Fiction, which has seen a rapid rise in popularity lately, particularly among the Young Adult crowd. This is not all too surprising, given the recent financial meltdown and increasing popularity of anti-establishment demonstrations such as Occupy Wall Street and the Tea Party protests. Steampunk and cybergoth is at an all-time high, and this chart barely scratches the surface of what's been written on the subject of oppressed societies and post-apocalyptic worlds. From Ayn Rand's Anthem and Atlas Shrugged to James Dashner's The Maze Runner and Jeanne DuPrau's The City of Ember, there is plenty to read in this genre, so long as books remain free! For more selections take a look at Wikipedia's List of Dystopian Literature.