Boys & Girls by LMC. Second Katekyo Hitman Reborn opening.
Hajimari no Sora, 11th Fairy Tail opening if I remember right. Aaaand then there's Masayume Chasing, the newest Fairy Tail (2014) opening.
..can't forget the first Soul Eater opening either omg. :DDD These four are my top four and I flip-flop on which I prefer since it depends on my mood at the time.
I really really like the 2nd Opening to Kill la Kill! It's soooooo gooooddddd. I was going to post a link here, but I can't find an opening that isn't pitched :(.