My PixelSkin HD!
Speck are my favourite, had a black CandyShell for my 3GS and a blue one for my iPod touch a few years ago! Hoping for a white PixelSkin HD or Candyshell for the new iPhone in a month and a bit...
I have a Pixelskin HD in red which I quite enjoy (been wanting to pick up a turquoise one as well), plus two Candyshells: the Cherry Blossom and the Year of the Dragon. Love them both, especially the dragon one.