I'm assuming Noah and Allie are the two main young characters. If that is so, Noah is being played by Ryan Gosling. He is a former Mouseketeer from the much missed 90s update of the Mickey Mouse Club. You may have seen him in the Sandra Bullock thriller Murder by Numbers (he played one of the killers and actually dated Bullock in real-life for a little bit) or in the phenomenal "The Believer" - a little seen flick in which he plays a Jewish teenager who denies his Jewish heritage and becomes a neo-Nazi. Incredibly powerful film that does not end happily, but Gosling won much praise and several awards for his portrayal which was based on a true story.
I work at a movie theater and several of my co-workers have seen "The Notebook" and have said great things about it.
RyMickey