7. Jason Isaacs
Look me in the face and tell me that Jason Isaacs isn't on everyone's wish list for the Master. He was put on this Earth to play the role. While he has a long and illustrious history of playing the villain, I think that his unique brand of dark humor and upper class entitlement is a perfect fit for the Master. And because the character only makes occasional appearances, he wouldn't have to worry about a major time commitment or scheduling conflicts. If the past few years have taught us anything, it's that Doctor Who is capable of getting big name actors for supporting roles (see John Hurt, Derek Jacobi, Michael Gambon, Bill Nighy,etc). He could just show up when he felt like it, be awesome for a little while, then go back to his life. How is this a bad plan?