In 2010 and 2011 the federal estate tax exemption was $5,000,000, and it increased to $5,120,000 in 2012 and $5,250,000 in 2013, which means that if an estate is valued at $5,250,000 or less and death occurs in 2013, then the estate will not owe any federal estate taxes. Below are links to charts that show the amount of the federal estate tax exemption from 1916 through 2013:
Chart Showing Federal Estate Tax Exemption: 1916 - 1997
Chart Showing Federal Estate Tax Exemption: 1997 - 2013
In addition, for 2011 and later years, the federal estate tax exemption has been made "portable" between married couples:

