The base corporate tax rate in the US is 35% with most companies paying an effective rate of 1.3% in 2011.
The republican nominees and the President are both proposing a move to 28% and all have said it will, of course, not add to the deficit (which is the issue of our time).
I hope some of the proposals come with some actual substance, ie. what types of corporate subsidies or tax loop holes will be cut in lieu of the new 28% deal.
My guess none will be forthcoming and of course, neither side will allow the other to pass this legislation through congress so its an election year promise that no future President will ever have to deliver.