In my WIP the US government has had a undetectable spy network since the '50's, so the political and economical area has changed. Picture the US holding the winning cards whenever they had to play hardball.
Key change is that Watergate never happened -they did bug the Democratic National Committee, but the break-in was never detected, letting Nixon complete his second term.
What I need is your most educated guesses on who could have been president after him and who could be the president today?
This is a fun question, but it leads to speculation. You don't need an expert, you just need a good dreamer.
If the US had complete spy supremacy, the Soviet Union would have collapsed a decade earlier, probably in the term of whoever came after Nixon. That could have been Gerald Ford (assuming Agnew still resigned after his own scandal), unless Ted Kennedy decided to run in 1976. I don't think any other Democrat -- Carter, Jerry Brown, or George Wallace -- could have won in 76 without the Watergate scandal as backdrop.
I believe your alternate universe revolves around George H.W. Bush. Ford made him the head of the CIA in 76. If Bush decided that he liked being the head of the most powerful spy agency on Earth, he might not have gone into politics. But if he decided to go into politics he would be unstoppable, and would likely have taken Reagan's place as the dominant Republican in the early 1980s. Bush is holding all the reins in your world. I would expect that his son, Dubya, would never go into politics. Dubya went into politics to do better than his 'failed' father; if his father never failed at anything, Dubya would probably continue being a rebel. Jeb might aim for the presidency, though.
Fast-forwarding to 2012, it's almost impossible to say who might be president now. A super-dominant CIA would have been able to assassinate the leaders of Iraq and Iran and would have caught Al Qaeda before they became a problem. There would still have been the Great Recession, although it might have come earlier. Things would not necessarily be better, although without the threat of terrorism I wouldn't say that they were worse.
Without any serious international problems, America might have become even more focused on social issues and the rising inequality of wealth than we are in the real world. The president would either be a sincere populist like John Edwards (although I doubt him, specifically, because of his character flaws) or a religious fundamentalist like Pat Robertson (although I doubt him because he's too old in 2012.)
I suggest you make up two characters, a populist and a fundamentalist, and decide for yourself how their campaign against each other would go.
All this is just my own opinion, of course. As I said, predicting the future (or alternate present) based on human decisions isn't science and doesn't require an expert. Just a little knowledge about people, and the ability to spin stories.