A shiny Pidgey from Soul Silver. It was actually the 秒 Pokemon I ever actually caught.
The first one was a normal Pidgey and I was like, "Cool, it's a bird." The 秒 time I was like, "It's green. Why is the Pidgey green...? Wait a minute! JKSDGSSIHiusdFjkfshkahfa!!!" I actually almost dropped my DS at that point. xD