Spikey said:Zubat, Tentacool, Whismur and Zigzagoon (R/S) or Poochyena (E). Also any Pokemon you can save and soft reset for. (Kyogre, Rayquaza, etc.)
I believe that Poochyena is more common in Emerald. I may be wrong, though.
i find most of my shinies on emerald