We need to move more towards simplicity and away from complexity. So much about our economy and society is moving in the opposite direction, the last thing the gov't should do is contribute to the problem. With a simpler code, you could get rid of IRS and replace it with more restrain agency that focuses primarily on going after a smaller number of tax evaders, which would be easier to catch and then prosecute as a result. Compliance would increase and there would be less gray area for "tax avoidance" and sheltering to occur.
As for the specifics my preferred plan going back several years centers around two or three rates with only two or three deductions (home mortage limited to first home, capped charitable giving and maybe one to incentivize energy efficiency), EITC and a health insurance tax credit; a corporate tax rate that is somewhere between 15% and 25% with few deductions (maybe one for energy efficiency and research related activities); and tax free saving and investing for middle and working class people.
I'm assuming that you would substantially increase the standard deduction and or personal exemptions if you are going to have only two or three rates. Having a bottom rate of 15% and no deductions would be a huge tax increase on the middle class.
Perhaps I should go the Mittens route, "That's not my plan". 
I have been leaning towards three rates lately as opposed to two. I left some details out out of the plan for purposes of concission and had typed up more specific posts only to just erase them in this thread over the previous few days.
I am certainly game for exempting the first $40,000 to $50,000 so as to untax income for living expenses. Combined with the EITC, most would have negative tax rates.
But isn't it true that Mitt Romney's "47%" are the people who already have negative tax rates? I don't know how keeping negative tax rates for the bottom half and cutting by almost half the taxes of the top half will not totally ruin revenues, even if you eliminate all the revenues and every dollar saved from the feds is wisely reinvested.
This 47% thing ignores federal payroll taxes. Payroll taxes are essentially income taxes levied only on wages and these payroll taxes have no exemptions: there is no standard deduction or personal exemption for them like there is on the federal income tax.
http://www.nytimes.com/2013/04/14/opinion/sunday/payroll-tax-returns-anyone.html
