Right now? I just read Song of Kali by Dan Simmons, that one is pretty remarkable. The Diamond Age by Neal Stephonson.
Of all time .... too early to tell. I've read hundreds of novels (I have the bookshelves full and packed Kindle to prove it) and I feel like I'm just breaking the surface.
I've read most of what is listed here and have a few comments -
Terry Goodkind and Robert Jordan - so derivative of Tolkien it makes it hard for me to form an interesting opinion, but I hated them. For original, strong fantasy try Ursula Le Guin and the Wizard of Earthsea books or the two Mythago Wood books by Robert Holdstock (these two only if you have an interest in mythology). Also, The Song of Ice and Fire series beginning with A Game of Thrones by George RR Martein is an incredibly entertaining read if you don't mind a lot of sex, violence, politics, and jumping povs. I'd recommend Song of Ice and Fire to anyone.
Stephen King - His characters and themes are very similar in the majority of his work. An excellent novelist but don't limit yourself to one author. Lovecraft is the perfect place to start for horror. I should state I'm almost finished with the first of the Dark Tower series and can't wait to continue.
Jim Butcher and the Dresden books - If easy to read entertaining as hell is more your suit consider the Prey series by John Sandford if you like the mystery and a cool protagonist, or John Scalzi and the Old Man's War books if you like the fantasy elements (though this is SF, they're similar reads).
I haven't read any video game fiction or magna (or whatever that Japanese stuff is called). While I'm sure there's real quality there, expand your horizons. SF and fantasy have a wide berth and great depth.
To the people that listed standard high school English class reads (I'm looking at you 1984) - keep reading and find literature forums. There's a whole world of literature out there that's very worth your time. If you do like distopian/speculative fiction/commentary on society and where it's going-type books, be sure to check out Fahrenheit 451, Brave New World, 1984, Animal Farm, and Margaret Atwood (in particular The Handmaid's Tale, though Oryx and Crake and The Blind Assassin are good too).
Finally who I am assuming are younger readers that listed Eragon, a Twilight book, and Harry Potter. KEEP READING. Books will change your life for the better and broaden your existence. Oh, and any girl worth your time will admire a well read man.
Oh, and House of Leaves is definitely NOT for everyone. I enjoyed it though, what a trip.