First Meeting: "Escape" by Enrique Iglesias
Oh my god.......  hilarious?  'You can run, you can hide, but you can't escape my love....'

First Dance: "Inara's Suite" by Greg Edmonson, from the Firefly Soundtrack
Awhh...  sweetness, slow, hidden, violin solo for a quiet dance somewhere no one will see? 

First Kiss: "Get in or Get out" by Hot Hot Heat
lol.  Bad fanfic anyone?  a first kiss in the middle of a half-hearted fight?  "make up your mind and get in or get out!"

Making Love Song:  "When the World Ends" by Dave Matthews Band from the Matrix Reloaded Soundtrack
well.. being as in order for this to actually happen on this ship, the world would pretty much HAVE to end....
Nice song for a 'before the end' type love scene?  "we're gonna dive into the emptyness, we'll be swimmin..."

First Fight:  Okay, the fact that I even have this song just speaks to my love of teen angst?  
"I Don't Wanna Be in Love" by Good Charlotte....
is this one of those 'erin chuckles to herself as the song pops up on the shuffle' moments?  Yes, I think it is...

Breakup Song: seems odd that wizards would break up to hip hop?  but the tone of the song is about right....
"Sweetest Girl" by Wyclef (feat. Akon), "but she feels no different after...."

Engagement Song: Oh... my... delicious angst?
"The Ghost of You" by My Chemical Romance.  This would be one of those 'let's get engaged while we're still alive' things...

Wedding Song: face it, it wouldn't happen?  So I guess this song would just be the rose-tinted imaginings of the more sentimental of the two (obviously Potter)?  lol, "Just a Touch of Love" by C+C Music Factory from the Sister Act Soundtrack?

Finale: the "oh well, I guess we survived the end, let's move on and be happy" music of a new day?
"Close Your Eyes" by the Chemical Brothers
"In your eyes I can see that you're cracking up, In your eyes I can see that you had enough... In your eyes I can see that you fell in love....  What if all that was coming to me, What if it all were to change?"