3. Loki & Red Skull
Arguably the two most sinister characters in the Marvel Cinematic Universe to date, it would be amazing to see these two teaming up as the founding members of a live action Masters of Evil. Both of them have an insatiable lust for power and, together, they could be formidable enough to succeed in truly attaining it. That said, the likelihood of them actually working seamlessly together - and not just using each other before turning against each other - is slim to zero and the ensuing battle between the two (especially if they had armies and/or items of power backing them up) could be truly epic. Red Skull appeared to be absorbed in to the Tesseract in the first Captain America movie, rather than actually perishing, so a return could be on the cards in a future movie and a meeting with Loki would really spice things up (though the likelihood of Hugo Weaving taking the role on again is almost non-existent).