My first level 100 was also my first Shiny legend-- A beautiful Shiny Rayquaza, straight from a Japanese copy!
I was really proud of it, despite the fact it's not EV'd or anything. It can still take down most In-Game teams by itself.
That, and it's a Shiny Legend. Now if that isn't something to be proud of, I don't know what is.
...Actually, thinking about it, most of my level 100s are the legendaries you catch at a high level... Huh, guess I'm pretty lazy. =P