Quick Google search using these indices:
<http://www.google.com/search?q=list+federal+rights+privileges+married+gay+couples>

which leads to lots of hits including
<http://www.religioustolerance.org/mar_bene.htm> Which is called,
"LEGAL AND ECONOMIC BENEFITS OF MARRIAGE"
From that page: "On the order of 1,400 legal rights are conferred
upon married couples in the U.S. Typically these are composed of about
400 state benefits and over 1,000 federal benefits."

<http://tinyurl.com/2rpyr> Leads to a heavy-duty report.
Representative Henry J Hyde (in 1996) was chairperson of the House
Committee on the Judiciary, and asked the General Accounting Office
"to identify federal laws in which benefits, rights and privileges are
contingent on marital status." Their response, which runs 75 pages, is
available online. <http://tinyurl.com/2rpyr>

It covers 13 types of laws:
     Social Security and Related Programs, Housing, and Food Stamps
        Veterans' Benefits
        Taxation
        Federal Civilian and Military Service Benefits
        Employment Benefits and Related Laws
        Immigration, Naturalization, and Aliens
        Indians
        Trade, Commerce, and Intellectual Property
        Financial Disclosure and Conflict of Interest
        Crimes and Family Violence
        Loans, Guarantees, and Payments in Agriculture
        Federal Natural Resources and Related Laws
        Miscellaneous Laws

Eye-opener, is the report.

Pastorio