Other than my deceased Skarmory trapped in a dead Gen 2 game, I have a shiny Sunflora. I use it on my sun team, because it's EVd and stuff, man. However, it uses Quiver Dance Pass support from my Venomoth, because Sunflora is slow as an actual sunflower.
The first shiny I came across was a Trainer's Espeon in Leaf Green. Later in the same game when on an Unown catching spree, I came across a shiny blue "A" Unown. My friend had a black Rayquaza but I'm convinced he cheated it in. Oh, and I caught a shiny Ryhorn once. Can't remember which game it was.