While I don't care for the Bible Black series very much, I have always adored the school uniforms. There's just something about the mix of black, white, and red for the color scheme that's very pleasing to the eye and eye-catching, and the cut and fit of the uniform is very flattering. I'd always intended to make myself one and finally got around to it for Katsucon '07!
This is the first "uniform" type cosplay I've done, and I love it because it's simple, cute, and extremely comfortable to wear. I don't have to bother with crazy costume pieces, wigs, or heavy props when I wear it, which is great for those days at conventions when I just don't feel like spending a lot of time in an elaborate costume. ^_^