Rent 'Terminator', watch it and keep in mind that the graphics aren't too fantastic but the story is good. Then see Terminator 2 - this movie will be one of your favorites, I promise. Finally, see Terminator 3.
Definately go see Finding Nemo, I'm 18 and I'm going to see it tonight, so don't worry about looking too young to be in the theatre.
All the other movies out don't really impress me, so I couldn't really suggest you see them.