If you have access to Wi-Fi, you could try putting up a monster for a Ditto and hope for a Japanese one, then breed it with whatever monster you want as a shiny.
I believe this negates the ability to pass down Natures, but drastically increases your chance at a shiny baby Pokémon.
These aren't actual figures, but I believe in Gen 4 it reduces likelihood from 1/8000 to roughly 1/2000.
It works better in Gen 5 though I believe, dropping to just over 1/1000.
Other than that, PokéRadar seems to work well (I got a shiny Shinx).
Just chain up to roughly 40 of the same monster and your chances are fantastically high of getting a shiny.