The just-released Statistics of Income Bulletin (Winter 2004-05) includes Individual Income Tax Returns, Preliminary Data, 2003, by Brian Balkovic (SOI).  Here is the summary:

For 2003, taxpayers filed 130.6 million U.S. individual income tax returns, an increase of 0.3% from the 130.2 million returns filed for 2002. For the first time in three years, AGI rose, increasing by 2.9% to $6.2 trillion for 2003.

For related tables of data, see here. For related individual income tax statistics, see here.