Although I haven't been very involved in the Harry Potter fandom for about 9 months now, I still love it terribly. I love the books, I love the fanfiction, I like the movies (kinda sorta). There are very few great crossovers between Harry Potter and Supernatural, however, even though I think these worlds lend themselves to nearly limitless possibilities for interacting.
I read Harry/Draco nearly exclusively in the HP fandom, though I've read Harry/Lucius and Harry/Volemort rather extensively as well. At one point I was even desparate enough to read Harry/Snape. Fortunately, before I went through too many fics in that pairing, I discovered J2 and Supernatural and spared myself the agony. (I would like to point out, just for the sake of clearing the air, that I mean no offense when I'm stating my personal dislike of Snarry. And I have in fact read a few well written and even believable Snarrys, but those are few and far between imo).
One of my favorite Harry/Lucius stories is Mulligan by Elpin. Occassionally, if I remember, I'll revisit author's journals and see if anything new has been happening. Which is how I discovered her fic God's Permission, a crossover between Supernatural and Harry Potter. (
http://elpin.livejournal.com/103024.html) I'm only on the second chapter of this WIP, but it promises to be interesting and it's well written.
I kind of found myself caught up in one line in the second chapter. Harry is thinking about the Winchester brothers, and pondering how their lives are similar, and the extraordinary paths destiny carved out for them all. And there's this line: "He wondered if his own fate would have been different if he had had a brother. A big brother to protect him, to help him, to protect him even?"
And now I want to read a story about just that. I know there have been a few well done fics featuring Harry with a brother, usually a twin. There have also been thousands, maybe tens of thousands, of horrificly written fiction in this category. But I'm not sure I remember seeing a fic where Harry is a younger brother, where the older brother isn't evil, isn't stealing the spotlight (isn't the BWL, in other words), and where canon remains fairly accurate. I would really love to read a story where Harry and this older brother survived the war into adulthood, and what their relationship might be like. I'd even read Harry/Ginny if it meant I could have this ;)
I know that there are sometimes fests for the Harry Potter fandom where readers can leave prompts. It's always been a little like visiting the Dr.'s office for me. I have questions, but when I'm sitting on the exam table I can't think of any. When I'm staring at a prompt form, I draw a blank. Hopefully next time I see an opportunity, I'll remember that I have an idea that hasn't been done often (or at least done well) and maybe inspire an author!