Memory/Friends/Graduation songs?

I'm working on a special project for my class this year as we are graduating and many of us have known each other for 9+ years so I want it to be really special! I have three songs picked out but i want a fourth too. So far I have 'Little Wonders' by Rob Thomas, 'I'll Always Remember You' by Hannah Montana, and 'Time of Your Life (Good Riddance)' by Greenday. I really want a song that will express the friendships we have made, the memories we've shared, and how much we mean to each other (aka: A LOT) I also want it to be fun and upbeat or soft, slow, and possibly sad ;) if you can find a song like that. Thanks!