http://thomas.loc.gov
The main informational web site of the U.S. Congress.  Contains summaries of bills and other useful legislative information

http://www.irs.gov/ep
IRS Employee Retirement Plans Site

http://www.dol.gov/ebsa/
Employee Benefits Security Administration

http://www.gpo.gov
The Government Printing Office

http://www.senate.gov
U.S. Senate

http://www.house.gov
U.S. House of Representatives

http://www.benefitslink.com
Extensive information on employee benefits plans, frequently updated