Here are some fanfics that I think are really great. They arent the cliched crappy fan fics but really have some substance. =D

Down From the Tree: Actions
This fan fic is brilliantly written and I think captures the emotions between the marauders which I love. It's taken from Snape's point of view, which is cool. and is probably my favorite fan fic other than the next one...
Rating:

Down From the Tree:Consequences
This is the sequel of Down From the Tree: Actions and is taken from Sirius's point of View. The first time I was practically crying while reading because you feel so sympathetic with Sirius especially when he's talking about Harry, James, and Lily. *blows nose* I really think that both of these are worth a read and they really do fit with the books nicely.

Darkness Dying: Strawberry Moon
This is another Marauders tale but focuses more on Peter and his reasoning for going to the dark side. I really thought this also fit with the series and gave us an understanding to what was actually going on with Peter. Although I still hate him (*growl*), this fan fic defenitely evokes some sympathy. =)