On 17 September 2007, Secretary of Energy Samuel W. Bodman announced that the U.S. will remove 9 metric tons of plutonium from its weapon stockpile. This most recent declaration is a 20 percent reduction of the amount of plutonium in the U.S. stockpile of plutonium assigned to the weapon program: the remaining inventory of weapon-grade plutonium is now 37.8 tons (see updated bar chart below).
Assuming a fissile material inventory of 4 kg in an average pit, the 9 tons would be equivalent to more than 2,000 nuclear warheads and the 36 tons remaining in U.S. pits that has not been declared excess would be equivalent to almost 10,000 warheads.
In 1995, the U.S. declared 45 tons of separated plutonium excess. Of that, 38.2 tons was weapon grade, of which 21.3 tons was actually in excess weapons or components at Pantex. This left 44.9 tons of weapon-grade plutonium in weapons and components at Pantex plus 1.9 tons of weapon-grade plutonium in other locations not declared excess. All this data is summarized in the DOE's 1996 publication Plutonium: The First 50 Years.
For a recent discussion of plutonium disposition efforts, see Chapter 3 of the Global Fissile Material Report 2007, Disposition of Excess Plutonium, lead-authored by Matthew Bunn (Managing the Atom, Harvard University).