-Just like Heaven (2005)- It is a romantic comedy, a guy moves into an apartment, only to find it haunted by a very... active spirit (Who is also the female lead). It rates in my mind as one of the funnier romantic comedies I have seen, but not the funniest. Notable enough that it came to mind when I first read you question though.
SHE'S THE MAN! well its not really a romantic movie but its so good just watch it and you ll remember me! also, channing tatum is in the movie so it can't be anything but perfect!;) haha
Addicted to Love Adult World The Philadelphia Story Gigi and even though it's not at all a romantic film, i absolutely adore the relationship between husband and wife Nick and Norah in the Thin Man Series.