I've had two extremely weird shiny incidents. Once in Soul Silver I found a shiny Spearow before I could obtain Poke Balls. Another time I was chaining for shiny Silcoon in Sinnoh, and I found a shiny Silcoon....as a random encounter. It wasn't a shiny patch, I would know, as I caught a Ralts in a shiny patch before.
Actually, the Rattata is female... ... ... Well color me yellow 'n call me Chinese, 'cause I am disappoint it ain't a boy. Guess I'll just kill it name it Josephine instead... T'is better than no reference t' that top percentage derpkid.
Caught a shiny Geodude (YES! A GOLD ONE!) in Platinum accidentally whilst trying to find a Hippopotas (Bloody 5% appearance rate). Don't want to evolve it as it turns into a brown Graveler and Golem.
I also have a shiny (Silver and Gold) Metang in Black 1.