U. S. Green Building Council
USGBC and LEED information. You should register on this site as soon as possible. Not only will you have access to valuable information, but the exam may have questions whose answers can only be found on this site.

Green Building Certification Institute
LEED exam information. This is the site that you will register for the exam.

Professional Publications Inc.
A great source of LEED study materials.

LEEDforum.org
A forum dedicated to the LEED rating systems and LEED exams.

AREforum
Another great forum, with a section for LEED topics.