From this Yahoo! story:

The United States has ceded to Russia and France last year its role of the top arms supplier to the developing world as it failed to take full advantage of emerging markets and opportunities created by booming oil prices, according to a new congressional study.

The annual report by the Congressional Research Service showed the US share of the arms transfer market dropped from 35.4 percent to 20.5 percent between 2004 and 2005.