4 come to my mind.
2 by the same director.

- The Thin Red line, and The New World. First time seeing, I didn't care for them AT ALL. I didn't care for the new world at all. But now I think back at it...and I really, really like it!!!!
I now consider the Thin Red Line one of the best movies I've seen.

Apocalypse Now is a good example too. I was bored by this movie in the cinema..long movie. like 200 minutes for the Redux version? But now, after seeing it again and again...I LOVE IT.

Alexander too. Didn't care for it the first time. Saw it again...and again. And now I love it.

It's basically lead me to hold the doctrine that unless a movie is obviously bad and/or right from the Hollywood assembly line, I won't criticize it fiercly unless I see it again.

i really like "l.a. confidential" now. it is really good.

Ditto with me and Alexander. Didn't like it in the cinema, now I'm a great fan!

Still find The New World far too slow and uneventful though...

Unforgiven
The Russia House

Um, Hearts in Atlantis comes to mind. I actually really liked it after I watched it a second time. Don't ask me why, I can't explain it.

28 Days Later...

Contact

Pirates of the Caribbean - didn't care for it at first, now I love it.
Same with The Aviator.

The Wicker Man ('73). Saw it when I was a little too young to appreciate it. Now it's one of my favorite cult titles.

Sling Blade, Arlington Road, Pulp Fiction.

Citizen Kane
Bridge on the River Kwai
I'm going to watch "Doctor Zhivago" tonight or tomorrow, I'm hoping I enjoy it more this time (I think I was way to young the first time I saw it)

Little Shop of Horrors ('86)

Citizen Kane
Eyes Wide Shut

This isn't as high brow as some of the other choices but one of the most drastic changes was with the recent "King Arthur". When I was a kid I LOVED the King Arthur myth, and read every version I could lay my hands on. I knew the way the story was supposed to go. For this reason I was insanely excited for and ultimately hated "Excalibur".

When I first heard about the new "King Arthur" movie I was dismayed at the "re-imagining" of the story, and avoided it at the theater. I saw it when it was first released on DVD and instantly loathed it, I couldn't even watch the second half. About 6 months ago a friend convinced me to watch it again, this time not thinking of it as a King Arthur movie, but just another sword/period flick.

This time I actually enjoyed it. I mean, it wasn't brilliant by any means, but it was fun and well made. Now I like the movie a lot and actually own it. As long as I close my eyes during the title credits, it's a fine movie.

Anyone have any more?

The obvious ones:

Apocalypse Now - I used to watched this in my younger days with friends, basically because we were severely under the influence of various things. Didn't get it, didn't even know anything about war really because it was off-limits growing up. Now that I'm older I can't see it enough, one of the top films ever for many reasons.

2001 - Pretty much the same, my older friends thought it was a masterpiece, I thought it was boring. In the past 5 years I've seen the light.

John Wayne movies, and pretty much most westerns. Still haven't warmed up to him or the genre that much, but I've grown to appreciate and enjoy some of the finer works like Stagecoach and The Searchers.

Brokeback Mountain....First film that came to mind when I read the thread title. I always liked it, but the first time I saw it in the theater I was kinda bored. But after seeing it again I really love this film and I can now appreciate the film's slower pacing.

Blade Runner. it's a movie that requires more than one viewing.

2001
Blade Runner

Fight Club. I was really bored right after he met tyler.

Martin Scorsese's "After Hours" really bored me the first time I saw it when I was in high school. Maybe, it had something to do with my buddy not liking it so I didn't like it. I saw it about 2 years later and thought it was very funny.

Anchorman. thought it was okay when I first saw it. saw it again on HBO and really enjoyed it.

Awesome movie. It's more-or-less been forgotten. But I always think of it when I think of 'great movies'.

Blue Velvet for me. I despised the movie when I was 16-or-so. And, yes, I do still have the same taste in movies that I had back then. There was just some unlikable about it. After I saw Mulholland Drive, I bought the Blue Velvet SE DVD and gave it another chance. From there, I was hooked on David Lynch movies.

I doubt you're alone on that one. I saw it in the theaters, and remember being mocked [on this forum] for likin' it so much.

Pulp Fiction. Didn't see it in its initial run and then got my expectations way up when I finally saw it on DVD years later. Saw it the first time, and wondered what the big deal was? Watched it again the next night just to see if I was missing anything, and loved it, and now think it is a great film. I don't know why this happens on the second viewing, but I am starting to believe if you go in with unbelievable expectations, chances they will not be met, and you won't like any film.