I would do away with the income tax and go with a national sales tax. I have never ever understood taxation of production.
Also, I would not allow pork barrel add-ons to bills. Each bill would be on its merits and its merits only. Why the hell is their funding for non-transportation issues in a transportation bill, for example?
I would scrap about half of the federal departments and programs, starting with welfare (all forms corporate and individual), and social security (or possible modify this very heavily). I would also modify the ADA to specifically exclude drug addicts, alcoholics and other forms of "social disabilities".
Finally, I would get rid of affirmative action legislation as it relates to hiring and firing personnel. I should be able to hire who I want when I want without the worry of reprisal. Yes, I would be stupid to pass up a better candidate based on his skin color or sexual preference, but that stupidity should be my decision.
*edit
One other thing, I would ban Congressperson's Pension Plans. They get elected once and end up making more money after retirement than they did during their stay in office. Oh and limit Secret Service only to past presidents. IIRC, Congressmen get the same luxury (but I could be wrong).