Heart Strings by Find Vienna. Seriously one of my fave songs at the moment, and the love montage video is just amazing! I can't even count all the awesomeness, Singing in the Rain, Moulin Rouge, I Love Lucy, Mickey & Minnie, The Sound of Music, Grease, Titanic, Boy Meets World, Mary Poppins, the list goes on. I even forgive them for the Twilight moment, because there are so many great movies/tv shows in there.
(If you're interested the Cory/Topanga moment comes at 2:44)