While there are lots to choose from, sometimes it can be very hard to find a HP fanfiction that I really love. Maybe I'm too picky; there have been many occasions where I've immediately stopped reading a fic upon seeing terrible grammar/punctuation/spelling and even bad formatting... but pickiness can pay off. Here are ten stories - in no particular order - that I always look forward to reading or have loved reading in the past.
Though a lot of people don't like OC fics, Harry Potter and the Girl Who Lived has an interesting concept. Harry is still very much the main character - in fact, in a way, this statement has never been truer - and finds himself amidst very strange circumstances in this story.
Now, I'm not a massive lover of Voldemort-before-he-was-Voldemort fics, but Somewhere Over The Rainbow is exceptional. It also features a lot of OCs, all of which I firmly believe to be canon whilst reading the story, because that's just how good it is.No HP list would be complete without some Severus action which Time's Fool has an abundance of. He and Hermione are written beautifully, and - if that isn't enough - this fic is like a hundred different stories in one, so you'll never get bored.
Lovers of Dramione should have at least heard of Obliviator, but if not, then there you go - done. It's an interesting original fic that captures Draco wonderfully - albeit not always positively, but hey, he's a git in canon for a good majority of the books.Another fic I love is Relationship Status Pending - it's different to your normal Hermione stories, because in this one she has terrible luck and is a lot more... provocative, I suppose. This fic made me laugh loads and at times cry buckets and has heaps of twists to make you dizzy... in a good way.
I have a great fondness for Neville's character, and You'll Be The Death of Me is a fantastic OC story that has never left me bored and has always left me wanting more. It's plot goes way beyond events in the canon books and explores a lot into the lives for Death Eaters' children.

So the concept behind this story has definitely been done before, but Chemistry & Timing has a neat little twist that makes me love it. It's a Remione time travel fic that keeps me wondering what's going to happen next and is delightfully in character.
For those that prefer a more light-hearted story involving (of course) the awesome Sirius as well as his brother Regulus, Bottle-Specs is pretty darn good. It's another OC fic, and there is something amazingly refreshing about her personality and behaviour.
If you're a fan of Fred, then Say Something is a fantastic Fremione story to read. Once again, it isn't an entirely new idea, but this story has a great twist that I have yet to see anywhere else and leaves me dying for more chapters.
Finally, I feel like I should mention The Irony, because although it is relatively new and there are perhaps more interesting fics out there, an update for this Sevmione story never fails to make me jump up and down. There is just something brilliantly charming about it, trust me.
As is probably obvious by now, I like reading fanfictions about either Hermione or OCs. I definitely prefer non-canon pairings too, but I digress. Hopefully there is at least one story here to intrigue you. All of these fics were a joy to read