Great.I went to edit my post with the list of songs I liked and it lost my post because it was more than 10 minutes to compile my list.
Season One:
Hallelujah--Jeff Buckley. Ryan is leaving Newport. Marissa is standing at the endof her driveway waiting for Luke to pick her up. He looks sad as he looks at her who is looking at him. (Exact same scene and song is used in the finale of the first season).
White Flag -- Dido. Ryan escorts Marissa out when she debuts in society. Very cute scene.
Space -- Something Corporate. When Ryan finds Marissa passed out in the alley in TJ. He carries her in his arms she is wearing a white dress type thing. (Same thing in the season 3 finale but different song!)
Dice -- Finely Quay and Beth Orton. Ryan rushes up the stairs to try to get to Marissa before its midnight to share a New Years Kiss. Perfect moment.
Wonderwall--Ryan Adams. Teresa finds out shes preggers. Marissa finds out and puts everything together. She dumps Ryan when he gets back.

Maybe I'm Amazed--Jem *The OC edit verison is sooooooooo touching* Marissa tells Ryan "I want you to know that I understand why you have to do this but I wish you didn't," as she cries and cries. Its such a sad scene to watch.
And then once again, Jeff Buckley. As we have the same scene from "The Model Home".
Season 2:
Only one song sticks out in my mind.
Hide and Seek-- Imogen Heap. The song is played during Caleb's funeral and agains after Marissa shoots Trey to save Ryan's life. If I'm not mistaken I think the song even plays DURING the last bit of their fight.
Season 3.
Hide Another Mistake -- The 88. When Ryan sees Trey at the bus stop.
Gangsters and Thugs -- The Transplants. When Jimmy is getting the crap beat out of him by the guy who he borrowed money from.
Salvation -- Black Rebel Motorcycle Club. Ryan and Marissa make love for the first time in some hut.
Baby Blue -- All Sad Girls Are Beautiful. When Marissa tells her father goodbye and if he is leaving he better be leaving for good because she can't handle the ups and downs with him and Julie.
Wasted --Black Flag. Johnny jumps. Sadness for some, Joy for me.
Friends -- Chris Holmes. The collage of their graduation.
Speeding Cards-- Imogen Heap. Marissa tells Ryan that shes leaving to go work on a boat with Jimmy and she'd like him to take her to the airport. "It only makes sense, I was the first person you saw when you got here, its only fitting you be the last person I see before I leave."
Chapters -- Appogee. The four of the kids go back to the Model Home and share a day of fun in the sun before saying their goodbyes.
Hallelujah--Imogen Heap. Marissa dies in Ryan's arms. Very sad scene. Very fitting song. Throw back to "The Escape" with Ryan carrying her from the wreckage and the white thing she is wearing (white flowy top I think) and the song from the season 1 finale but by a different group.
Ummm yeah, I was a REAL huge fan of the show until they killed off Marissa. Its just hard, you kill off my favorite character I find it hard to watch the show.