What are some Harry Potter fanfiction ideas?

Answer 1

Harry and Fred get bitten by a mad basilisk and then they become the same person. After which, Mad Eye Moody and Professor Flitwick get married and honeymoon in an Albanian forest where they meet Lord Voldemort riding a unicorn.

Hopefully this has shown you that an author needs to invent their own ideas -- here's a link to help you with that. If you're going to be a writer, you need to think on your own, not ask some anonymous person on the internet to write your stories for you!

Some of the most common ones (meaning: try to avoid them):

- Snape is Harry's father/stepfather/mentor

- Two of Snape, Draco and Harry (or all three of them) are lovers

- Harry has got a twin sister (author avatar) or a twin brother (spoiled brat)

- Bellatrix Lestange has a daughter who is good (author avatar) and falls in love with Neville

- Forced marriage (often by Marriage Law)

- Harem: Harry marries lots of girls

- Peggy Sue: a character travels back in time and makes things better

- Azkaban: Harry is unjustly locked into the Azkaban, which somehow makes him extremely powerful

- Original character (author avatar) joins the canon plotline, perhaps become the main protagonist

- Original female character's love story with Snape/Sirius/Lupin/Draco/...

- Fluff without Plot

- Porn without Plot

(the last two are the most common, obviously)

Answer 2

The Tales of Beedle the Bard.