My favorite romantic scene in anime has to be when Edward basically professed his love for Winry at the end of FullMetal Alchemist Brotherhood. This is just a fan drawing and not the actual scene but it's great nonetheless.
This is the actual scene; Ed just kinda hugs Winry which was always disappointing to me but still nice. "Equivalent Exchange, I'll give you half of my life if you give me half of yours" that's kinda how I want to purpose marriage. @VinMcCarthy