Being someone who is extremely musically inclined, I didn't see a topic like this, so I figured I'd start one.
Post your favorite Touhou songs, remixes/arranges included.
http://www.youtube.com/watch?v=VIop055eJhUU.N. Owen Was Her?, one of my favorite songs in the entire series, partially because it was my first Touhou song. It fits as a childish person who has horrible power, but doesn't consciously understand what she's doing. I particularly like the music box-esque tune from 0:19 - 0:31.
http://www.youtube.com/watch?v=A_vtVahCYRkThe first Touhou remix I ever heard, Common State of Innocent Violence, an arrange of Flandre's theme. It evokes Flandre's raw destructive power more than her childlike innocence.
http://www.youtube.com/watch?v=v0XF9a7EQSMHeart Under Blade, by one of my favorite arrangers, Kokuyasou/Black Night Funeral. I like it for the same reasons as Common State of Innocent Violence, and it has basically the same tone.
http://www.youtube.com/watch?v=lac01jcCSSsThe One Who Inherits the Scarlet Craze (紅い狂気の継承者), by ARA. Not much to say about it, but it's good.
http://www.youtube.com/watch?v=oxC0nXJu71ICool&Create's arrange of U.N. Owen Was Her?. I like it more as a song than as a representation of Flandre's character, personally.
http://www.youtube.com/watch?v=sEM9mdqFpU4U.N. Owen Was Her? by 砂塵音樂室. I like it for the same reasons as Cool&Create's arrange, but I particularly like what they did with the music box-esque portion I mentioned.
http://www.youtube.com/watch?v=vo9HjGn0T20悪魔の妹と4台のピアノのための極めて破壊的な狂騒曲, by Xe. One of my favorite U.N. Owen arranges, it perfectly demonstrates the innocence, anger, hopefulness, sadness, and raw power that I feel form Flandre's character.
http://www.youtube.com/watch?v=tFQX4pjQ4-4Another favorite of mine, Unknown? by Mistyhaze, which is also the only song they've done that I actually like. It evokes the same feelings as the previous song in the list, I think, but in its own, unique way.
http://www.youtube.com/watch?v=UE2khbsBMos緋色月下、狂咲ノ絶 by EastNewSound. I have mixed feelings about this one: I really like it, but I can't decide if it fits Flandre's character or not. Seems like it does to an extent.
http://www.youtube.com/watch?v=7Vz2AEJFVtgNearly my favorite arrange of Flandre's theme, Sweets Time Midnight. A perfect representation of Flandre's character. There isn't much more to say.
http://www.youtube.com/watch?v=5Zfy6cUo1wMOne of TAMusic's arranges of U.N. Owen Was Her?, and easily my favorite version of that song. It's really just perfect in so many ways.
...I promise I'll post later with songs other than U.N. Owen Was Her?, seriously.