The best thing I've heard to actually curb the president's power is McCain's proposal to force the president to be questioned by opposition in the congress... like they do in parliamentary democracies (it would also be nice to switch over to a parliamentary system... but it's not going to happen... run-off elections are also on my wish list... but Santa's just not answering).
If the president were held to greater scrutiny in the public eye rather than, for all practicality, framing the most of politics for the average American, it would greatly control executive power.
Transparency and accountability are the way to go.

__________________
"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside