I love post-it notes. You seem to brainstorm the same way I do.

But, as Brandi said, I use a digital post it board.

Here's my more organized one (from last year):
http://linoit.com/users/SarahRae/canvases/NaNo2015

And my quick brainstorming I did over the last couple days, so it's not organized:
http://linoit.com/users/SarahRae/canvases/Unblessed