All you want to know about GRE
Sample GRE questions and free online study materials:
You can get some example GRE papers from ets.org site. Here is the link.
Here are some other best places to get some online study material for GRE:
GRE PowerPrep 3.0 by 'ETS'
Click to Download
Full-length Computer Adaptive GRE test by
Math section practice test by '800score.com'
GRE practice software by 'Petersons'
GRE Bulletin, Sample questions, etc from 'GRE.org'
Click to visit the download page