Dratini/Dragonair - Change them to have the same colors as Dragonite.
They're one of my favorites! I was actually coming in here to say that I'd change Dragonite's shiny colors to be the same as its pre-evolutions, lol. They're very pretty.
Otherwise.... almost any green shiny, to a better/more pleasant shade of green. Most of them, especially Espeon, look really bad.
Also, shiny Arcanine should be white! That would look amazing. And Cinccino's shiny should be link like Minccino. :<