U.S. Department Of Justice
http://www.usdoj.gov

U.S. Department of Labor (DOL)
http://www.dol.gov

Department of Labor Library: Immigration Collection
http://www.oalj.dol.gov./libina.htm

Social Security Card
All you need to know about social benefits in the USA
http://www.ssa.gov/howto.htm

US customs
What are you allowed to bring with you or take out of the USA?
http://www.customs.gov/travel/travel.htm

INS-Statistics
This is a great site for people interested in statistics. All possible statistics in regards to US immigration can be found here.
http://www.ins.usdoj.gov/graphics/aboutins/statistics/index.htm

American Presidents
A description of all past and present Presidents of the United States
http://www.ipl.org/ref/POTUS/