There's a lot of really, really good HP fic but it can be a mission to find it! I remember when marriage law fics were all the rage, Neville/Draco is actually the Chosen One, all the flashbacks to the 70s, Harry travels back in time to X period...

From memory, there was a big shift when GoF came out (since there was such a large gap between it and OotP that there was a massive surge of fics) and then OotP ruined a lot of fanon.