Another nice trick that early retirees might be able to pull off is to pay no income taxes on traditional 401(k) and IRA contributions and withdrawals.
What's the catch? You retire early, have a very low taxable income, and each year you do a Roth contribution with those traditional balances, up to the point where you hit the 10% Federal tax bracket. For a single taxpayer, this could be in the neighborhood of $10,000 - $20,000 annually depending on your personal circumstances, dividend interest income, deductions, etc. If you do this, then you pay 0% going in and 0% going out.
Of course, with a relatively low income you might not have to pay much taxes when you withdraw the traditional contributions anyway, but if you can gradually transfer these balances into Roth anyway, you might as well do it.