Here is a quick overview of the NSF GRFP from the NSF GRFP official site http://www.nsfgrfp.org/
Fellows share in the prestige and opportunities that become available when they are selected. Fellows benefit from a three-year annual stipend of $30,000 along with a $10,500 cost of education allowance for tuition and fees, opportunities for international research and professional development, and the freedom to conduct their own research at any accredited U.S. institution of graduate education they choose.
I was a successful applicant in 2010, and the thing that was most helpful was reading example essays from award winners. In the spirit of giving back, I have posted mine online on my website and found others who have done the same.
List of example essays:
Physics (me) http://www.alexhunterlang.com/nsf-fellowship
Environmental Science http://rachelcsmith.com/academics/nsf.htm
Computer Science http://jxyzabc.blogspot.com/2008/08/cs-grad-school-part-3-fellowships.html
Synthetic Engineering http://openwetware.org/wiki/User:Kaull/NSF
If anyone else knows of example essays (especially physics examples), please post a link below and/or let me know and I'll add a link to my website. I will keep updating my website with new example essays and periodically post updates to this thread.