Stuff that's romantic but good story at same time:
Cinema Paradisio
Casablanca
The Illusionist
Big Fish
Don Juan DeMarco (omg Johnny Depp..the hotness!)
Princess Bride
Stuff that's scary (so she'll grab yer arm, giggidy)
My Bloody Valentine 3D (ok, not so much scary but funny/gross/classic horror plot) and watch it in 3D to get the full experience. It's even funnier if you watch it and pretend that the main murder is the Pyro from TF2 (Hudda hudda huh!)
The Orphanage
Just plain good
Mirrormask
Repo! The Genetic Opera (ok, so this belongs in the "scary" because it's gory and made from the makers of Saw...but it's a rock opera too, so...I don't know how to describe it. It's good though!)
Star Trek (even if she's not a Trekkie, it's a fun one)
Little Miss Sunshine
Pan's Labyrinth
Chronicles of Narnia: Prince Caspian
Um...that's all I can think of right now. I'm tired. It depends on her tastes. You should know what kinds of stuff she likes to watch, boyfriend. ~_^