For me, it would have be the Amulet of Time series by Luna the Moonmonster. The stories are definitely cliche'd by now. But the world building she did, the ability to actually complete many of the stories in the series and all the different times she went to were pretty awesome to me during the time that she updated them.

What I loved about them is that they were the first fics I found that had Time Travel into the WWII era and the Founders era. The last story she worked on even had the group being sent to Ancient Egypt, which was original at the time.

Her stories are why I love the time travel genre in fanfiction.

 

I still remember the ending of Dance with me Harry
http://www.fictionalley.org/authors/aerie22/DWMH.html

It was one of the first fics I have read after Barb's trilogy, and it was new then.

 

I still remember Drip and Drop. And I can't even remember the title of the story. The rape and bloody murder and the murder and bloody rape. Someone help me out here. Possibly the best unhinged Harry.

The Blood Tipped Feather by QuaziJoe that has the entire world finding out about magic via flying/angel Harry(?) on television. That was the most memorable, "muggles find out magic is real! zomg," moment. And the fallout of that. I remember it as epic. Although I couldn't tell you what all happens now.

Temptations of a Dark Soul. Explodra. Need I say more?

There is also a "Voldemort takes Harry into his camp and tries to recruit him by treating him like a prince and then Harry gets along with Draco and..." I think this was the first fic I read that made Draco into a likable character for me. The title had the word amulet IIRC. I've been searching for it now but have not found it. I saw it in the DLP archive (the download) a long time ago and don't know whether it's online still. If anyone knows the title or it rings any bells let me know.

 

This reminds me of a story named "HP and the Trelawney Prophecy".
Edit: found it. I'm linking the author's page as it's a series: http://www.fictionalley.org/authors/krysroz/

 

The moment I realised that I have already read all good stories of fandom and new ones was coming at dripping speed.

Coincidentally that was around the time I have started to branch out to other fandoms.