I'm going to assume you're not willing to crossplay/dress so...
Lilly and Hanako or Shizune and Misha from Katawa Shoujo.
Patty and Liz from Soul Eater (Bonus if you can get a 3rd to be Kid)
Mariya and Matsurika from Maria Holic
Any two female Vocaloids
and the list goes on and on
Gakuen Hetalia, Prussia (Shado 12)
Pokemon, Gold/Ethan (Shado 12, Metro 13)
Vocaloid, Dell Honnie
Batman, Black Mask
Soul Eater, Spirit/Death Scythe (Shado 12, Metro13)
Hetalia, England Cd (Metro 13)
Team Fortress 2, Blu Spy
Soul Eater, Giriko
Vocaloid, Big Al
Space Wolf, Warhammer 40k