Through careful allocation between our IRAs and Roth IRAs, my wife and I adjusted our AGI to just below $35.5K, which is the phase-out point for the Saver's Credit, and were able to use said credit to drop our (W-2) tax liability to zero. (My wife had a small amount of 1099 income for which the $350 in self-employment tax was not deductible, hence the $350 / ~$35K = 1% effective rate.)
The best part is that it made our Roth contributions this year completely tax-free, including principal!
My challenge for the next year will be to do the same thing, but with a significantly higher gross income and significantly higher retirement account contribution to match.