Kurosaki and Shirosaki (Ichigo - Bleach)
Yugi and Yami-Yugi
Me Myself and Irene - Hank and Charlie (Jim Carey)
Your mom - She has times where she wants it upfront and den other times where she wants it in the back. :l

Akito/Agito (there is a third one, but you doesnt get to see that one in the anime) form Air gear
One is kinda gayish
And the other one is a deamon
Both of them are in the same person!