Economic Growth Act of 2008 - Amends the Internal Revenue Code to: (1) repeal the dollar and other limitations on the expensing allowance of depreciable business assets; (2) reduce to 25% the maximum corporate income tax rate; (3) provide for an inflation adjustment to the basis of certain capital assets for purposes of determining gain or loss; and (4) reduce from 35 to 15% the alternative capital gains tax rate for corporations.