See here for a copy of the November 7, 2002 32-page memorandum by Pamela F. Olson, then-Assistant Treasury for Tax Policy (now at Skadden, Washington, D.C.), to Treasury Secretary Snow. Here is the Introduction:

We have developed a paper stating the case for why the current tax system must be reformed as well as five options for fundamental tax reform:  a flat consumption tax, a flat income tax, an add-on value-added tax (VAT), an income value-added tax (IVAT) with Social Security integration, and reform of the current income tax.

(Thanks to Scott Hodge, President of the Tax Foundation, for the tip.)