Oops, I saw this earlier and then promptly forgot about it after going into the debate thread!
Here are my picks:
"Between the Lines" by Carrie: http://absolutechaos.net/viewstory.php?sid=9179This is my favorite AU and the story that made me truly appreciate how good AUs can be. It's about the guys as Seattle Mariners baseball players, which seems pretty random, but it's perfect because the brotherly bond they have as bandmates in real life works for them as teammates, too. The story progresses through one memorable season, and you see their bond with each other and their families/significant others, too. All five guys get a starring role, so it's definitely a group story, and their personalities make them seem like the same lovable guys we write fanfics about. It'll make you laugh and cry.
"Happenstance" by Bianca: http://absolutechaos.net/viewstory.php?sid=5453This is one of the rare romances I've read and enjoyed that doesn't rely on a lot of outside drama to make a good story. It's about Nick, who is just a regular guy living in a small town on the coast of North Carolina, and he literally runs into an older, married woman, and they have a summer romance/affair. It's very Nicholas Sparks. If you read romance outside of fanfic, it's worth checking out, because it's very well-written and reads like a non-trashy romance novel.
"On the Outside" by Amy: http://www.angelfire.com/ny2/dreamcastle/ontheoutside.htmI never would have read this story if it hadn't been for Mare and her old fanfic discussion group, but I did for that, and I ended up really enjoying it. It's a story inspired by "The Outsiders" about the guys as kids/teenagers who are orphaned or don't come from good families, living in poverty or on the streets, and they form a friendship and help each other to survive. It's been a long time since I've read it, so that's probably not a great summary of it, but I remember it being well-written and kinda cute, and again, it builds that brotherly bond well.