All you need is love...

[Brinniel]

Also, I think the song "Come What May" really fits for the Aragorn/Arwen relationship. Just see for yourself:

Never knew, I could feel like this
Like I've never seen the sky before
Want to vanish inside your kiss
Everyday I love you more and more

Listen to my heart
Can you hear it sing?
Telling me to give you everything
Seasons may change
Winter to spring

But I love you
Until the end of time

[CHORUS]
Come what may
Come what may
I will love you
Until my dying days

Suddenly, the world seems such a perfect place
Suddenly, it moves with such a perfect grace
Suddenly, my life doesn't seem such a waste
It all revolves around you

And there's no mountain to hide
No river to wide
Sing out this song and I'll be there by your side
Storm clouds may gather
And storms may come out

But I love you
Until the end of time

[CHORUS]

Some of the words may be off, but I think I did pretty good, considering it was done completely from memory.