Similar movies to Avatar that fans might like.
 

Star Wars Saga.
Star Trek movies.
Heavy Metal.
The Dark Crystal.
Total Recall
Starship Troopers.
Dune (1984, 2000 and Children of Dune).
The Fountain.
The Fifth Element.
Dark City.
2001 and 2010.
Fire and Ice (1983 animated Ralph Bakshi).
Beowulf.
Wizards.
Ghost in The Shell.
Princess Mononke.
Time Machine (1960 and 2002).
Atlantis The Lost Empire.
The Matrix Trilogy.
Titan A.E.
Alien Saga.
Pandorum.
Terminator 1 & 2.
The Island.
Starchaser Legend of Orin.
Lifeforce.
Outland.
Inception.
Transforners 1986, part 1 2007 and part 2.
Flash Gordon.
Barbarella.
The Cell.
The Black Hole.
Pitch Black.
LOTR Trilogy.

That, that is quite a list. :)

I've seen most of them, but you forgot Event Horizon, Mel Gibson's Apocalypto, and the TV series Andromeda, imo. (That series deserves a movie, although most people don't like it due to crappy soundtrack and story, I believe it goes deeper than that.)

I like, Saving private Ryan, BoB, The Last Samuri (spelling?), The Other Guys, Step up 2, Terminator series, Star Wars, any action movie really...

Moon and The Truman Show are two that instantly came my mind. I know some more movies but I just need to remember them first :P

Add an "A" between "R" and "I" ;)

I remember seeing Pitch Black when I was little. Very good movie... or at least that's what I remember. :P

Remembered some :)

Forest Gump
Back to the Future 1 -3
Indiana Jones (minus Kingdom of the Crystal Skull)
Kill Bill 1 and 2

Sunshine
The Abyss

all I could think of right now :P

Lots of good ones there. Lots of good ones added as well. Some I like

Last of the Mohicans
Dances with Wolves
Never Cry Wolf
V for Vendetta

Thats it for now.

I cannot believe nobody said District 9 yet....

I LOVE Princess Mononoke I think everyone should watch that movie atleast once. I grew up watching it and I still do watch it from time to time. The movie has a lot of the same things like tree spirits etc.

Hayao Miyazaki's films, good stuff :D

Um...every movie by M. Knight Shyamalan ever(except Airbender :P terrible movie).

Whoa, a big list. I haven't seen all of those.

I agree with the most, disagree with a few.

Do you agree or disagree on the similar movies i mentioned?