In some ways Richard Nixon is a Macbeth because he wished to eliminate his enemies before he became president in his second term (Watergate Scandal), and he became paranoiac. A tragic figure, Nixon was a good ruler with a successful first term; however, his "vaulting ambition" led to his seizing greater executive power. After his resignation, some of this executive privilege was removed.
Anyone who does an evil deed for personal gain could be considered a modern-day Macbeth. This would be especially true if the evil deed was influenced by outside sources (like the witches and Lady Macbeth in the play). Bernie Madoff and his scheme to embezzle from investors comes to mind.
It's hard to think of anyone who fits Macbeth's exact profile, although Hitler, Stalin, and Idi Amin have been suggested in previous answers to a similar question (see link below). Among very recent figures, I know that some people would compare Macbeth to George W. Bush for the following reasons:
1. They would claim that he came to power illegitmately, in the 2000 election.
2. They would claim that he felt as if he almost deserved the job of president, or was destined for it, because his father had been president.
3. They would claim that he did great evil during his presidency.
4. They would say that by the end of his term of office his presidency had essentially collapsed and that he wasn't sure what to do in response.
5. They would say that by the end of his term he had won the contempt and hatred of many people.
6. They would say that he was replaced by a far better figure.
I do not mean to indicate at all that I personally think that George W. Bush was comparable to Macbeth, but surely there are many people who would see similarites between the two. Still, it is hard to think of Laura Bush as in any way comparable to Lady Macbeth. Bush's critics would probably cast Dick Cheny in that role.