The first epic I remember seeing was Gone with the Wind in the Paramount Theater in Abilene. Getting out of a movie way past midnight was really cool. I also remember driving with friends to Fort Worth to see the new Cinescope epic How the West Was Won. Is the definition of an epic any movie that lasts over 3 hours?
My favorite would have to be Dr. Zhivago. It is one of the most beautifully cinemagraphed (is there such a word?) movies ever made. All that snow! And the history, and the love story! Wow!
A very close second would Lord of the Rings and Stars Wars, although they have a quite different slant. Harry Potter might be included, but his are not long enough.
I even enjoyed The Alamo. An earlier epic I enjoyed was Exodus. That's when I first fell in love with Paul Newman. Sam understood.