I have had quite a bit of luck with shinies during the years, and disregarding RNG'd or Masuda methoded.
I don't know if I saw any in GSC as I never knew about them. Lol. Aside from Gyarados, of course.
In Sapphire I remember catching a Lotad, and then notcing every other Lotad I saw was a totally different colour - and my friend pointed out to me that I had a 'shiny'. :D I was so excited.
Later in the game I cought a Shiny Wingull.
Since then I've seen heaps of shinies. Well, not heaps, about 10 (Metapod, Shroomish, Tentacool, Shinx, Staravia, Houndour and Geodude that I can remember) and just recently I've seen both a shiny Piloswine (giant chasm) and shiny Karrablast.