One time I wasn't even hunting, I just ran into a shiny pidgey in the grass before the first gym. Went back to the PC to check it out, came back to the grass, very next encounter, another shiny pidgey. I was like 'What sorcery is this?!"
I've hatched a shiny Tyrunt and Litleo, and a growlithe I gave away...
I've also had decent success in Safari's. All by accident, I got a shiny Gabite, Ponyta and Bergmite. Still trying to trade the Bergmite. It's got perfect IVs in Def and HP, so it could make a decent tank...
Y has been my lucky game for shinies. ^-^