My fav twins:
-Kagami and Tsukasa Hiiragi from Lucky Star:
Not identical (they even say so in the anime). Tsukasa is the shorter haired one.
-Ryou and Kyou Fujibayashi from Clannad:
They are identical twins, but one grew her hair out. In an OVA she cuts her hair and they are exactly the same)..Oh except their eyes, One's a Tsundere, so they have to make her look it lol Ryou is the shorter haired one
I found a picture that actually has both pairs on it..lol
I also thing the Tweedles, Dee and Dum are a good one lol they have so many versions that you can make your own up as long as you have the propeller hats and nametags to make it funny, as well as the thing 1&2 lol But also, there are series that have characters with versions..Like take the series No Game No Life, they gave the Werebeast, Izuna, 2 versions. They are clearly different as they are even different hair colors, but it's still obviously her. Things like that are always fun to see done.