New Earth: This is the Earth with the primary continuity after Infinite Crisis
Earth-2: The Justice Society Earth --the Huntress on this earth is the Daughter of the Batman. Reminiscent of Pre-Crisis Earth-Two.
Earth-3: The Crime Society's earth.
Earth-4: Blue Beetle, Captain Atom, and the Question, among others, are the heroes of this Earth. Reminiscent of Pre-Crisis Earth-Four.
Earth-5: The Marvel Family are Earth's main heroes on a world of magic. Reminiscent of Pre-Crisis Earth-S.
Earth-8: The world of Lord Havok and the Extremists.
Earth-10: The original Freedom Fighters fight Nazi counterparts of the JLA. (Originally Earth-X pre-Crisis.)
Earth-12: A future world inhabited by a version of Batman 'beyond anything ever seen'. (Batman Beyond)
Earth-13: Earth-Vertigo. (Unconfirmed.)
Earth-15: A world whose heroes have evolved to become 'nearly perfect beings'. [Appears to consist of junior heroes/sidekicks who have taken over for their mentors (Jason Todd has succeeded Batman, Zod is Superman and Kyle Rayner is formally a Green Lantern and not Ion).
Earth-17: A post-apocalyptic world where the Atomic Knights protect the last signs of life.
Earth-18: A world where the JLA are a group of lawmen who ride the Wild West. (The Justice Riders)
Earth-19: Batman fights Jack the Ripper in the 1880s. (Gotham By Gaslight)
Earth-21: A world where the Cold War has recently ended, and a new age of heroes has begun. (New Frontier)
Earth-22: A near-future world brought to the brink of apocalypse by warring superheroes. Starman confirms that before he came back to the 21st Century during the Lightning Saga, he was accidently shunted to Earth-22. (Kingdom Come)
Earth-26: Home of the cartoon animal superheroes Captain Carrot & The Zoo Crew.
Earth-30: Superman is a champion of Cold War-era Soviet Russia. (Superman: Red Son)
Earth-31: A "darker version of the future" seen in Superman/Batman.
Earth-32: Bruce Wayne becomes Green Lantern instead of Hal Jordan. (In Darkest Knight)
Earth-33: An Earth where magic rules, ie Batmage.
Earth-34: Wonder Woman in 19th century Britain against Jack the Ripper. (Wonder Woman : Amazonia)
Earth-40: Costumed heroes and villains currently in World War II. (The Liberty Files)
Earth-43: A world of vampires and the supernatural, inhabited by a vampire Batman. (Red Rain)
Earth-48: Native home of the Forerunners, creatures bred by the Monitors from all the alien races of the solar system after the destruction of all human life on Earth in a war against other planets.
Earth-50: Wildstorm Universe.
Still to be numbered offically :
Earth-Tangent, Earths based on The Nail, Thrillkiller and the gender-switched Superwoman/Batwoman one-shot.
Note to self : general wiki entry here