This year it's April 23, three days sooner than last year. From this Yahoo news story.

Americans will have to work on average 74 days to cover federal taxes, and another 39 days to cover state and local taxes, the group said. Housing costs require 60 days of work, while health care requires 50 days and food 35 days, it said.

The report and cool graph are here.

Tax Freedom Day is the cow bell, but elsewhere the Tax Foundation does some very good work, and has for over 70 years now.